Turnover Rate Constants Research Articles

Changes in Photosystem II Complex and Physiological Activities in Pea and Maize Plants in Response to Salt Stress.

Salt stress significantly impacts the functions of the photosynthetic apparatus, with varying degrees of damage to its components. Photosystem II (PSII) is more sensitive to environmental stresses, including salinity, than photosystem I (PSI). This study investigated the effects of different salinity levels (0 to 200 mM NaCl) on the PSII complex in isolated thylakoid membranes from hydroponically grown pea (Pisum sativum L.) and maize (Zea mays L.) plants treated with NaCl for 5 days. The data revealed that salt stress inhibits the photochemical activity of PSII (H2O → BQ), affecting the energy transfer between the pigment-protein complexes of PSII (as indicated by the fluorescence emission ratio F695/F685), QA reoxidation, and the function of the oxygen-evolving complex (OEC). These processes were more significantly affected in pea than in maize under salinity. Analysis of the oxygen evolution curves after flashes and continuous illumination showed a stronger influence on the PSIIα than PSIIβ centers. The inhibition of oxygen evolution was associated with an increase in misses (α), double hits (β), and blocked centers (SB) and a decrease in the rate constant of turnover of PSII reaction centers (KD). Salinity had different effects on the two pathways of QA reoxidation in maize and pea. In maize, the electron flow from QA- to plastoquinone was dominant after treatment with higher NaCl concentrations (150 mM and 200 mM), while in pea, the electron recombination on QAQB- with oxidized S2 (or S3) of the OEC was more pronounced. Analysis of the 77 K fluorescence emission spectra revealed changes in the ratio of the light-harvesting complex of PSII (LHCII) monomers and trimers to LHCII aggregates after salt treatment. There was also a decrease in pigment composition and an increase in oxidative stress markers, membrane injury index, antioxidant activity (FRAP assay), and antiradical activity (DPPH assay). These effects were more pronounced in pea than in maize after treatment with higher NaCl concentrations (150 mM-200 mM). This study provides insights into how salinity influences the processes in the donor and acceptor sides of PSII in plants with different salt sensitivity.

In vivo assessment of β-hydroxybutyrate metabolism in mouse brain using deuterium (2 H) MRS.

To monitor the metabolic turnover of β-hydroxybutyrate (BHB) oxidation using 2 H-MRS in conjunction with intravenous administration of 2 H labeled BHB. Nine-month-old mice were infused with [3,4,4,4]-2 H4 -BHB (d4 -BHB; 3.11 g/kg) through the tail vein using a bolus variable infusion rate for a period of 90 min. The labeling of downstream cerebral metabolites from the oxidative metabolism of d4 -BHB was monitored using 2 H-MRS spectra acquired with a home-built 2 H surface coil on a 9.4T preclinical MR scanner with a temporal resolution of 6.25 min. An exponential model was fit to the BHB and glutamate/glutamine (Glx) turnover curves to determine rate constants of metabolite turnover and to aid in the visualization of metabolite time courses. Deuterium label was incorporated into Glx from BHB metabolism through the tricarboxylic acid (TCA) cycle, with an increase in the level of [4,4]-2 H2 -Glx (d2 -Glx) over time and reaching a quasi-steady state concentration of ∼0.6± 0.1 mM following 30 min of infusion. Complete oxidative metabolic breakdown of d4 -BHB also resulted in the formation of semi-heavy water (HDO), with a four-fold (10.1 to ∼42.1± 7.3 mM) linear (R2 = 0.998) increase in its concentration by the end of infusion. The rate constant of Glx turnover from d4 -BHB metabolism was determined to be 0.034 ± 0.004 min-1 . 2 H-MRS can be used to monitor the cerebral metabolism of BHB with its deuterated form by measuring the downstream labeling of Glx. The integration of 2 H-MRS with deuterated BHB substrate provides an alternative and clinically promising MRS tool to detect neurometabolic fluxes in healthy and disease conditions.

Photocatalytic Behavior of Supported Copper Double Salt: The Role of Graphene Oxide

The design of a photocatalyst that may work efficiently with sunlight is a fundamental concern to fight against environmental pollution and electrochemical hydrogen storage devices. In this work, it has been found that the green microwave-assisted decoration of graphene by copper double salt (DS) enhances visible sunlight photocatalysis efficiency. Nanohybrids of graphene oxide decorated with Cu(I) and Cu(II) oxides and copper hydroxy nitrate double salt were selected as photocatalysts for the degradation of rhodamine B in aqueous solution to study the effect of the graphene oxide support. The photodegradation process followed a pseudo–first-order kinetics for the bare catalysts, but the supported catalysts were best fitted to the Langmuir-Hinshelwood model. Supported systems were more efficient in terms of turnover and apparent rate constants. Diffuse reflectance spectroscopy with the use of Kubelka-Munk function allowed to measure bandgap energies. It was found that the absorption edge was reduced about 30% for the supported systems.

Microbial Growth and Organic Matter Cycling in the Pacific Ocean Along a Latitudinal Transect Between Subarctic and Subantarctic Waters

The Pacific Ocean constitutes about half of the global oceans and thus microbial processes in this ocean have a large impact on global elemental cycles. Despite several intensely studied regions large areas are still greatly understudied regarding microbial activities, organic matter cycling and biogeography. Refined information about these features is most important to better understand the significance of this ocean for global biogeochemical and elemental cycles. Therefore we investigated a suite of microbial and geochemical variables along a transect from the subantarctic to the subarctic Pacific in the upper 200 m of the water column. The aim was to quantify rates of organic matter processing, identify potential controlling factors and prokaryotic key players. The assessed variables included abundance of heterotrophic prokaryotes and cyanobacteria, heterotrophic prokaryotic production (HPP), turnover rate constants of amino acids, glucose, and acetate, leucine aminopeptidase and β-glucosidase activities, and the composition of the bacterial community by fluorescence in situ hybridization (FISH). The additional quantification of nitrate, dissolved amino acids and carbohydrates, chlorophyll a, particulate organic carbon and nitrogen (POC, PON) provided a rich environmental context. The oligotrophic gyres exhibited the lowest prokaryotic abundances, rates of HPP and substrate turnover. Low nucleic acid prokaryotes dominated in these gyres, whereas in temperate and subpolar regions further north and south, high nucleic acid prokaryotes dominated. Turnover rate constants of glucose and acetate, as well as leucine aminopeptidase activity, increased from (sub)tropical toward the subpolar regions. In contrast, HPP and bulk growth rates were highest near the equatorial upwelling and lowest in the central gyres and subpolar regions. The SAR11 clade, the Roseobacter group and Flavobacteria constituted the majority of the prokaryotic communities. Vertical profiles of the biogeochemical and microbial variables markedly differed among the different regions and showed close covariations of the microbial variables and chlorophyll a, POC and PON. The results show that hydrographic, microbial, and biogeochemical properties exhibited distinct patterns reflecting the biogeographic provinces along the transect. The microbial variables assessed contribute to a better and refined understanding of the scales of microbial organic matter processing in large areas of the epipelagic Pacific beyond its well-studied regions.

Kinetics of myelin breakdown products: A labeling study in patients with progressive multiple sclerosis.

The majority of disease modifying therapies for multiple sclerosis (MS) reduce inflammation, but do no’t target remyelination. Development of remyelinating therapies will benefit from a method to quantify myelin kinetics in patients with MS. We labeled myelin in vivo with deuterium, and modeled kinetics of myelin breakdown products β‐galactosylceramide (β‐GalC) and N‐Octadecanoyl‐sulfatide (NO‐Sulf). Five patients with MS received 120 ml 70% D2O daily for 70 days and were compared with six healthy subjects who previously received the same procedure. Mass spectrometry and compartmental modeling were used to quantify the turnover rate of β‐GalC and NO‐Sulf in cerebrospinal fluid (CSF). Turnover rate constants of the fractions of β‐GalC and NO‐Sulf with non‐negligible turnover were 0.00186 and 0.00714, respectively, in both healthy subjects and patients with MS. The turnover half‐life of β‐GalC and NO‐Sulf was calculated as 373 days and 96.5 days, respectively. The effect of MS on the NO‐Sulf (49.4% lower fraction with non‐negligible turnover) was more pronounced compared to the effect on β‐GalC turnover (18.3% lower fraction with non‐negligible turnover). Kinetics of myelin breakdown products in the CSF are different in patients with MS compared with healthy subjects. This may be caused by slower myelin production in these patients, by a higher level of degradation of a more stable component of myelin, or, most likely, by a combination of these two processes. Labeling myelin breakdown products is a useful method that can be used to quantify myelin turnover in patients with progressive MS and can therefore be used in proof‐of‐concept studies with remyelination therapies.

Identification and quantification of distinct active sites in Hf-Beta zeolites for transfer hydrogenation catalysis

Despite the significant progress made in characterizing different framework heteroatom sites that exist in Lewis acidic zeolites with probe molecule adsorption and spectroscopy, methods to reliably quantify site counts remain indefinite and have been primarily limited to Sn and Ti Lewis acid sites. Here, methods to quantify framework Lewis acidic Hf4+ sites in zeolite Beta (Hf-Beta) with two Lewis base titrants (pyridine, deuterated acetonitrile) were developed using infrared (IR) spectroscopy. Lewis acid site counts for Hf-Beta zeolites were validated by measuring integrated molar extinction coefficients (IMECs; ε, cm μmol−1) on Sn-Beta zeolites using identical Lewis base titrants to benchmark site counts with established literature procedures to quantify Lewis acid sites in Beta zeolites from IR spectra. Highlighting the importance of benchmarking active site counts against well-established experimental protocols, IMECs of CD3CN bound to open (ε(Sn; 2316 cm−1): 1.80 ± 0.25) and closed (ε(Sn; 2308 cm−1): 3.76 ± 0.33) Sn sites were ∼ 1.8x larger than those previously reported while total Lewis acid site counts agreed with those measured by pyridine (ε(Sn; 1451 cm−1): 1.58 ± 0.16) on six different Sn-Beta zeolites. IMECs measured for IR peaks reflecting pyridine bound to Lewis acidic Hf sites (ε(Hf; 1448 cm−1): 1.54 ± 0.21) and CD3CN bound to open (ε(Hf; 2313 cm−1): 2.40 ± 0.22) and closed (ε(Hf; 2307 cm−1): 3.55 ± 0.41) Hf sites, gave similar counts for the total number of Lewis acidic sites across six Hf-Beta zeolites (Si/Hf = 100–413). Consistent with previous reports with Sn-Beta catalysts where open Sn sites are responsible for catalytic turnover, apparent first and zero-order MPVO rate constants (0.01–1 M cyclohexanone in 2-butanol; per total Hf, 373 K) correlated with the total number of open Hf sites, per total Hf, but not with the total number of closed Hf sites or total Lewis acid site counts. Measured initial MPVO rates (0.1 M cyclohexanone in 2-butanol, per open Hf, 373 K) were ∼ 25x higher on hydrophobic Hf-Beta-F than on hydrophilic Hf-Beta-OH zeolites. Overall, the apparent first-order MPVO rate constants (2-butanol solvent, per open Hf, 373 K) were ∼ 6x higher on Hf-Beta-F than on Hf-Beta-OH zeolites. The characterization methods reported here enable normalization of MPVO turnover rates on Sn- and Hf-Beta zeolites by their number of open sites. This enables performing quantitative rate comparisons across Lewis acid zeolites of varying active site identity, solvation, and pore topology used in liquid-phase catalysis.

Monoculture or Mixed Culture? Relevance of Fine Root Dynamics to Carbon Sequestration Oriented Mangrove Afforestation and Restoration

Fine root dynamics have the potential to contribute to ecosystem biogeochemical cycling, especially for carbon. This is particularly true in mangroves which are the most productive and carbon-rich ecosystems of the world. However, few studies comprehensively evaluated the contribution of mangrove fine root dynamics to soil organic carbon accumulation. In southern China, while the introduced fast-growing Sonneratia apetala and native shrubby Kandelia obovata have been widely used in mangrove reforestation/afforestation programs since the mid-1980s, their implications and ecosystem services are still unclear. Here we show distinct differences in fine root dynamic among 12-year-old S. apetala, K. obovata monocultures, and their mixed stand using root coring, ingrowth core, and intact-core methods. Soil organic carbon storage was examined by soil coring method. One-year observation showed significant differences among the three mangrove plantations in fine root biomass, necromass, turnover rate, and decomposition decay rate constant. Soil organic carbon stock was 15.8 ± 0.8, 7.8 ± 0.5, and 11.9 ± 1.6 Mg C ha–1 for K. obovata, S. apetala monocultures and their mixed stand, respectively. Live fine root biomass, fine root necromass, annual fine root production and fine root mass decay rate constant are significantly correlated to soil organic carbon content across plantations. We suggest that mangrove fine root dynamics were mainly affected by soil nutrient conditions and species composition. Mixed stands may not have higher soil organic carbon storage than monocultures. The functional trait of different mangrove species is responsible to determine the carbon storage function of mixed stands. Fine roots play an important role in carbon storage, and fine root dynamics have a significant effect on carbon sequestration in mangrove ecosystems. The shrubby native K. obovata had a higher potential for belowground carbon sequestration and storage than the tall introduced S. apetala.

Nucleoside selectivity of Aspergillus fumigatus nucleoside-diphosphate kinase.

Aspergillus fumigatus infections are rising at a disconcerting rate in tandem with antifungal resistance rates. Efforts to develop novel antifungals have been hindered by the limited knowledge of fundamental biological and structural mechanisms of A.fumigatus propagation. Biosynthesis of NTPs, the building blocks of DNA and RNA, is catalysed by NDK. An essential enzyme in A.fumigatus, NDK poses as an attractive target for novel antifungals. NDK exhibits broad substrate specificity across species, using both purines and pyrimidines, but the selectivity of such nucleosides in A.fumigatus NDK is unknown, impeding structure-guided inhibitor design. Structures of NDK in unbound- and NDP-bound states were solved, and NDK activity was assessed in the presence of various NTP substrates. We present the first instance of a unique substrate binding mode adopted by CDP and TDP specific to A.fumigatus NDK that illuminates the structural determinants of selectivity. Analysis of the oligomeric state reveals that A.fumigatus NDK adopts a hexameric assembly in both unbound- and NDP-bound states, contrary to previous reports suggesting it is tetrameric. Kinetic analysis revealed that ATP exhibited the greatest turnover rate (321±33.0s-1 ), specificity constant (626±110.0mm-1 ·s-1 ) and binding free energy change (-37.0±3.5kcal·mol-1 ). Comparatively, cytidine nucleosides displayed the slowest turnover rate (53.1±3.7s-1 ) and lowest specificity constant (40.2±4.4mm-1 ·s-1 ). We conclude that NDK exhibits nucleoside selectivity whereby adenine nucleosides are used preferentially compared to cytidine nucleosides, and these insights can be exploited to guide drug design. ENZYMES: Nucleoside-diphosphate kinase (EC2.7.4.6). DATABASE: Structural data are available in the PDB database under the accession numbers: Unbound-NDK (6XP4), ADP-NDK (6XP7), GDP-NDK (6XPS), IDP-NDK (6XPU), UDP-NDK (6XPT), CDP-NDK (6XPW), TDP-NDK (6XPV).

Promiscuous activity of 3-isopropylmalate dehydrogenase produced at physiological level affords Escherichia coli growth on d-malate.

Promiscuous activities of enzymes may serve as starting points for the evolution of new functions. However, most experimental examples of promiscuity affording an observable phenotype necessitate the artificial overexpression of the target enzyme. Here, we show that 3-isopropylmalate dehydrogenase (IPMDH), an enzyme involved in leucine biosynthesis, has a secondary activity on d-malate, which is sufficient for d-malate assimilation under physiological conditions where the enzyme is upregulated. Invitro, the turnover constant (kcat ) of IPMDH for d-malate is about 30-fold lower than the kcat for 3-isopropylmalate, yet sufficiently high to support the growth on d-malate. From an evolutionary perspective, our results highlight the possibility of phenotype emergence triggered by arbitrary changes in environmental conditions and prior to any mutational event.

A Kinetic Model for Glucose Levels and Hemoglobin A1c Provides a Novel Tool for Individualized Diabetes Management.

Regular assessment of glycated hemoglobin (HbA1c) is central to the management of patients with diabetes. Estimated HbA1c (eHbA1c) from continuous glucose monitoring (CGM) has been proposed as a measure that reflects laboratory HbA1c. However, discrepancies between the two markers are common, limiting the clinical use of eHbA1c. Therefore, developing a glycemic maker that better reflects laboratory HbA1c will be highly relevant in diabetes management. Using CGM data from two previous clinical studies in 120 individuals with diabetes, we derived a novel kinetic model that takes into account red blood cell (RBC) turnover, cross-membrane glucose transport, and hemoglobin glycation processes to individualize the relationship between glucose levels and HbA1c. Using CGM data and two laboratory HbA1c measurements, kinetic rate constants for RBC glycation and turnover were calculated. These rate constants were used to project future HbA1c, creating a new individualized glycemic marker, termed calculated HbA1c (cHbA1c). In contrast to eHbA1c, the new glycemic marker cHbA1c gave an accurate estimation of laboratory HbA1c across individuals. The model and data demonstrated a non-linear relationship between laboratory HbA1c and steady-state glucose and also showed that glycation status is modulated by age. Our kinetic model offers mechanistic insights into the relationship between glucose levels and glycated hemoglobin. Therefore, the new glycemic marker does not only accurately reflect laboratory HbA1c but also provides novel concepts to explain the mechanisms for the mismatch between HbA1c and average glucose in some individuals, which has implications for future clinical management.

Lipidome-wide 13C flux analysis: a novel tool to estimate the turnover of lipids in organisms and cultures

Lipid metabolism plays an important role in the regulation of cellular homeostasis. However, because it is difficult to measure the actual rates of synthesis and degradation of individual lipid species, lipid compositions are often used as a surrogate to evaluate lipid metabolism even though they provide only static snapshots of the lipodome. Here, we designed a simple method to determine the turnover rate of phospholipid and acylglycerol species based on the incorporation of 13C6-glucose combined with LC-MS/MS. We labeled adult Drosophila melanogaster with 13C6-glucose that incorporates into the entire lipidome, derived kinetic parameters from mass spectra, and studied effects of deletion of CG6718, the fly homolog of the calcium-independent phospholipase A2β, on lipid metabolism. Although 13C6-glucose gave rise to a complex pattern of 13C incorporation, we were able to identify discrete isotopomers in which 13C atoms were confined to the glycerol group. With these isotopomers, we calculated turnover rate constants, half-life times, and fluxes of the glycerol backbone of multiple lipid species. To perform these calculations, we estimated the fraction of labeled molecules in glycerol-3-phosphate, the lipid precursor, by mass isotopomer distribution analysis of the spectra of phosphatidylglycerol. When we applied this method to D. melanogaster, we found a range of lipid half-lives from 2 to 200 days, demonstrated tissue-specific fluxes of individual lipid species, and identified a novel function of CG6718 in triacylglycerol metabolism. This method provides fluxomics-type data with significant potential to improve the understanding of complex lipid regulation in a variety of research models.

The mineralization characteristics of organic carbon and particle composition analysis in reconstructed soil with different proportions of soft rock and sand.

The organic carbon mineralization process reflects the release intensity of soil CO2. Therefore, the study of organic carbon mineralization and particle composition analysis of soft rock and sand compound soil can provide technical support and a theoretical basis for soil organic reconstruction (soil structure, materials and biological nutrition). Based on previous research, four treatments were selected: CK (soft rock:sand=0:1), C1 (soft rock:sand=1:5), C2 (soft rock:sand=1:2) and C3 (soft rock:sand=1:1), respectively. Specifically, we analyzed the organic carbon mineralization process and soil particle composition by lye absorption, laser granulometer, and scanning electron microscope. The results showed that there was no significant difference in organic carbon content between C1, C2 , and C3 treatments, but they were significantly higher than in the CK treatment (P < 0.05). The organic carbon mineralization rate in each treatment accords with a logarithmic function throughout the incubation period (P < 0.01), which can be divided into a rapid decline phase in days 1 to 11 followed by a steady decline phase in days 11 to 30. The cumulative mineralization on the 11th day reached 54.96%–74.44% of the total mineralization amount. At the end of the incubation, the cumulative mineralization and potential mineralizable organic carbon content of the C1, C2 and C3 treatments were significantly higher than those of the CK treatment. The cumulative mineralization rate was also the lowest in the C1 and C2 treatment. The turnover rate constant of soil organic carbon in each treatment was significantly lower than that of the CK treatment, and the residence time increased. With the increase of volume fraction of soft rock, the content of silt and clay particles increased gradually, the texture of soil changed from sandy soil to sandy loam, loam , and silty loam, respectively. With the increase of small particles, the structure of soil appear ed to collapse when the volume ratio of soft rock was 50%. A comprehensive mineralization index and scanning electron microscopy analysis, when the ratio of soft rock to sand volume was 1:5–1:2, this can effectively increase the accumulation of soil organic carbon. Then, the distribution of soil particles was more uniform, the soil structure was stable (not collapsed), and the mineralization level of unit organic carbon was lower. Our research results have practical significance for the large area popularization of soft rock and sand compound technology.

Effects of long-term fertilization on soil organic carbon mineralization and microbial community structure.

Soil microorganisms play a pivotal role in carbon mineralization and their diversity is crucial to the function of soil ecosystems. However, the effects of long-term fertilization on microbial-mediated carbon mineralization are poorly understood. To identify the relative roles of microbes in carbon mineralization of yellow paddies, we investigated the long-term fertilization effects on soil properties and microbial communities and their relationships with carbon mineralization. The treatments included: no fertilization (CK), chemical fertilizer (NPK), organic fertilizer (M), and constant organic-inorganic fertilizer (MNPK). NPK treatment significantly increased soil water content (WC), while M and MNPK treatments significantly increased the content of soil organic carbon (SOC), total nitrogen (TN), soil microbial biomass carbon (SMBC), soil microbial biomass nitrogen (SMBN), and WC. Strong increases in CO2 emissions, potential mineralized carbon, and turnover rate constant were observed in both organic-fertilizer treatments (M and MNPK), relative to the CK treatment. These changes in soil properties can be attributed to the variation in microbial communities. NPK treatment had no significant effect. Different fertilization treatments changed soil microbial community; SOC and SMBN were the most important contributors to the variance in microbial community composition. The variations in community composition did not significant influence carbon mineralization; however, carbon mineralization was significantly influenced by the abundance of several non-dominant bacteria. The results suggest that SOC, SMBN, and non-dominant bacteria (Gemmatimonadetes and Latescibacteria), have a close relationship to carbon mineralization, and should be preferentially considered in predicting carbon mineralization under long-term fertilization.

High-Throughput Measurement of Lipid Turnover Rates Using Partial Metabolic Heavy Water Labeling.

Novel analytical platforms for high-throughput determination of lipid turnover in vivo have been developed based on partial metabolic 2H2O labeling. The performance on lipid kinetics measurement of our methods was validated in three different liquid chromatography-mass spectrometry (LC-MS) setups: MS-only, untargeted MS/MS, and targeted MS/MS. The MS-only scheme consisted of multiple LC-MS runs for quantification of lipid mass isotopomers and an extra LC-MS/MS run for lipid identification. The untargeted MS/MS format utilized multiple data-dependent LC-MS/MS runs for both quantification of lipid mass isotopomers and lipid identification. An in-house software was also developed to streamline the data processing from peak area quantification of mass isotopomers to exponential curve fitting for extracting the turnover rate constant. With HeLa cells cultured in 5% 2H2O media for 48 h, we could deduce the species-level turnover rates of 108 and 94 lipids in the MS-only and untargeted MS/MS schemes, respectively, which covers 13 different subclasses and spans 3 orders of magnitude. Furthermore, the targeted MS/MS setup, which performs scheduled LC-MS/MS experiments for some targeted lipids, enabled differential measurement between the turnover rates of the head and tail groups of lipid. The reproducibility of our lipid kinetics measurement was also demonstrated with lipids that commonly detected in both positive and negative ion modes or in two different adduct forms.

Population pharmacodynamics of cilostazol in healthy Korean subjects.

Cilostazol is used for the treatment of intermittent claudication, ulceration and pain. This study was conducted to develop a population pharmacodynamic (PD) model for cilostazol's closure time (CT) prolongation effect in healthy Korean subjects based on a pharmacokinetic (PK) model previously developed. PD data were obtained from 29 healthy subjects who participated in a study conducted in 2009 at Severance Hospital. The PK model used was a two-compartment model with first order absorption. CT data were best described by a turnover model with a fractional turnover rate constant (Kout) inhibited by drug effects (Eff), which were represented by a sigmoid Emax model [Eff = Emax · Cγ / (EC50γ+Cγ)] with Emax being maximum drug effect, EC50 drug plasma concentration at 50% of Emax, C drug plasma concentrations, and γ the Hill coefficient. For the selected PD model, parameter estimates were 0.613 hr−1 for Kout, 0.192 for Emax, 730 ng/ml for EC50 and 5.137 for γ. Sex and caffeine drinking status significantly influenced the baseline CT, which was 85.36 seconds in male non-caffeine drinkers and increased by 15.5% and 16.4% in females and caffeine drinkers, respectively. The model adequately described the time course of CT. This was the first population PD study for cilostazol's CT prolongation effect in a Korean population.

Quantitative analysis of the effect of end-tidal carbon dioxide on regional cerebral oxygen saturation in patients undergoing carotid endarterectomy under general anaesthesia.

Regional cerebral oxygen saturation (rSO2 ) is currently the most used measure in clinical practice to monitor cerebral ischaemia in patients undergoing carotid endarterectomy (CEA). Although end-tidal carbon dioxide (PET CO2 ) is known as a factor that influences rSO2 , the relationship between PET CO2 and rSO2 has not been quantitatively evaluated in patients with severe arteriosclerosis. This study aimed to evaluate the effect of PET CO2 on rSO2 in patients undergoing CEA under general anaesthesia. The intervention to change PET CO2 was conducted between skin incision and clamping of the carotid artery. The rSO2 values were observed by changing PET CO2 in the range of 25-45mmHg. The PET CO2 -rSO2 relationship was characterized by population analysis using a turnover model. In total, 1651 rSO2 data points from 30 patients were used to determine the pharmacodynamic characteristics. Hypertension (HTN) and systolic blood pressure (SBP) were significant covariates on the slope factor in the stimulatory effect of PET CO2 on rSO2 and fractional turnover rate constant (kout ), respectively. The estimates of the parameters were kout (min-1 ): 3.59 for SBP<90mmHg and 0.491 for SBP ≥90mmHg, slope: 0.00321 for patients with HTN and 0.00664 for patients without HTN. The presence of HTNattenuates the response of rSO2 after a change in PET CO2 . When cerebral blood flow is in a state of decline caused by a decrease in SBP to <90mmHg, the response of rSO2 to PET CO2 is increased. It is advisable to maintain SBP >90mmHg in patients with HTNduring CEA.

Estimating decay dynamics for enzyme activities in soils from different ecosystems

Extracellular enzymes in soil are central to the decomposition of plant and microbial detritus and they are increasingly incorporated into soil biogeochemical models as drivers of detritus breakdown. In enzyme-driven models, a critical parameter is the functional lifespan of the enzymes, yet this is poorly constrained by experimental data. We evaluated how long soil enzymes remain active in five soils spanning from arctic tussock tundra to a tropical forest/grassland soil. We incubated soils under continuous fumigation with CHCl3 vapor to kill microbes and prevent the synthesis of new enzymes. We monitored the activities of six hydrolytic and two oxidative enzymes over a 12-week incubation. Initial activities of the various soil enzymes varied substantially across the ecosystems; they were generally highest (per gram soil) in the tussock tundra, followed by temperate hardwood forest, grassland, tropical forest/grassland, and then chaparral. In tussock tundra organic soil, activities of all enzymes decreased rapidly following first-order decay curves; the half-lives of enzyme activity were typically several weeks. In the mineral soils, the time course of loss of hydrolytic enzyme activities could always be described by a first-order decay curve, but in many cases, activity could equally be described by a zero-order, linear, decay function because the rate of loss was slow. Although α-glucosidase lost activity rapidly, for other enzymes substantial activity remained even after 12 weeks of incubation. This likely resulted from stabilization by mineral surfaces, stabilization that might constrain activity against native polymeric substrates. Measured turnover rate constants fell within the broad range that model have used, but that range remains exceedingly broad.

Gaussian Process Modeling of Protein Turnover.

We describe a stochastic model to compute in vivo protein turnover rate constants from stable-isotope labeling and high-throughput liquid chromatography-mass spectrometry experiments. We show that the often-used one- and two-compartment nonstochastic models allow explicit solutions from the corresponding stochastic differential equations. The resulting stochastic process is a Gaussian processes with Ornstein-Uhlenbeck covariance matrix. We applied the stochastic model to a large-scale data set from (15)N labeling and compared its performance metrics with those of the nonstochastic curve fitting. The comparison showed that for more than 99% of proteins, the stochastic model produced better fits to the experimental data (based on residual sum of squares). The model was used for extracting protein-decay rate constants from mouse brain (slow turnover) and liver (fast turnover) samples. We found that the most affected (compared to two-exponent curve fitting) results were those for liver proteins. The ratio of the median of degradation rate constants of liver proteins to those of brain proteins increased 4-fold in stochastic modeling compared to the two-exponent fitting. Stochastic modeling predicted stronger differences of protein turnover processes between mouse liver and brain than previously estimated. The model is independent of the labeling isotope. To show this, we also applied the model to protein turnover studied in induced heart failure in rats, in which metabolic labeling was achieved by administering heavy water. No changes in the model were necessary for adapting to heavy-water labeling. The approach has been implemented in a freely available R code.

Exploring the kinetic and thermodynamic aspects of four-electron electrochemical reactions: electrocatalysis of oxygen evolution by metal oxides and biological systems.

Finding fundamental and general mechanisms for electrochemical reactions, such as the oxygen evolution reaction (OER) from water and reduction of CO2, plays vital roles in developing the desired electrocatalysts for facilitating solar fuel production. Recently, density functional theory (DFT) calculations have shown that there is a universal scaling relation of adsorption energy between key intermediate species, HO(ad) and HOO(ad), on the surface of metal oxides as OER electrocatalysts. In this paper, a kinetic and thermodynamic model for the four-electron electrochemical reaction based on previous OER mechanisms proposed by DFT calculations is developed to further investigate the electrocatalytic properties over a wide range of metal oxides and photosystem II. The OER activity of metal oxides (i.e. electrocatalytic current) calculated from the DFT-calculated equilibrium potentials with kinetic properties, such as the rate constants for interfacial electron transfer and catalytic turnover, can lead to a volcano-shaped trend that agrees with the results observed in experiments. In addition, the kinetic aspects of the impact on the electrocatalysts are evaluated. Finally, comparing the results of metal oxides and photosystem II, and fitting experimental voltammograms give further insights into kinetic and thermodynamic roles. Here, the general guidelines for designing OER electrocatalysts with unified kinetic and thermodynamic properties are presented.

Modelling and determination of metabolic pools by stable carbon isotopes in the avian duodenal mucosa and albumen.

Stable isotope analyses have helped in assessing dietary switches if the diet undergoes metabolic alteration (isotopic exchange). However, when considering the effects over time of switching from one diet to another, one can assess how quickly the new diet is incorporated into tissues via the isotopic renewal or incorporation rate, or turnover. Turnover is obtained using exponential curves that fit the original data, allowing the determination of practical order parameters such as the half-life (T) and the turnover constant (k). Researchers have found that metabolic incorporation can be fractionated. The resulting fractions, called metabolic pools, are identified using the linearization of the isotopic exchange model and its linear fit. This fractionation methodology is still not well defined. The objective of this study was to assess the behaviour of the metabolic renewal rate (turnover) in fractionated form, explain the theory, and apply it to data from the avian duodenal mucosa and albumen. We concluded that the duodenal mucosa has one metabolic pool, with a half-life of 1.23days, and that the albumen has two metabolic pools, with half-lives of 1.89 and 6.32days.