Maximal Reduction Rate Research Articles

Visual Evoked Potential Can Predict Deterioration of Visual Function After Direct Clipping of Paraclinoid Aneurysm With Anterior Clinoidectomy.

The role of visual evoked potential (VEP) in direct clipping of the paraclinoid internal carotid artery (ICA) aneurysm remains uncertain. To examine whether intraoperative neuromonitoring with VEP can predict deterioration of visual function after direct clipping of the paraclinoid ICA aneurysm with anterior clinoidectomy. Among consecutive 274 patients with unruptured cerebral aneurysm, we enrolled 25 patients with paraclinoid ICA aneurysm treated by direct clipping after anterior clinoidectomy with intraoperative neuromonitoring with VEP in this study. We evaluated the visual acuity loss (VAL) and visual field loss (VFL) before surgery, 1 month after surgery, and at the final follow-up. The VAL at 1 month after surgery (VAL1M) and VAL at the final follow-up (Final VAL) were significantly related to the reduction rate of VEP amplitude at the end of surgery (RedEnd%), more than 76.5%, and the maximal reduction rate of VEP amplitude during surgery (MaxRed%), more than 66.7% to 70%. The VFL at 1 month after surgery (VFL1M) and the VFL at the final follow-up (Final VFL) were significantly related to MaxRed% more than 60.7%. VAL1M, Final VAL, VFL1M, and Final VFL could be significantly predicted by the value of RedEnd% and MaxRed% in direct clipping of Al-Rodhan group Ia, Ib, and II paraclinoid ICA aneurysms with anterior clinoidectomy.

Growth Inhibition Kinetics of Acetonitrile Biodegradation

As the most pristine and one of the biggest continents in the southern hemisphere, Antarctica has over the decade accumulated hydrocarbon pollution mainly due to human activities related to logistics and transportation in this area. Acetonitrile spills caused by the sinking of the cargo ships call for research into acetonitrile-degrading microorganisms in the form of bioremediation in order to be ready for disasters in the future. The efficiency of a previously isolated acetonitrile-degrading sludge consortium as a bioremediation technique has been demonstrated. However, as the acetonitrile concentration rises, its growth was severely restrained. Acetonitrile's inhibitory effect on this consortium's development rate is modeled in this work using the Luong, Aiba, Haldane, Hans-Levenspiel, Yano, Teissier and Monod models. Statistical evaluations indicated that the most suitable kinetic model to fit the growth rate on acetonitrile was the Teissier-Edwards’s model. The computed values for the Teissier constants like maximal reduction rate (max), half saturation constant for maximal degradation (Ks) and half inhibition constant (Ki) were 0.934 1/H (95% confidence interval 0.301 to 1.567), 1.504 g/L (95% confidence interval 0.877 to 2.131), and 4.574 g/L (95% confidence interval 2.764 to 6.383), respectively. The parameters obtained from this study will be beneficial in acetonitrile biodegradation works.

Substrate Inhibition Kinetics Models for Fitting the Growth Rate of Phenol by an Immobilized Pseudomonas putida

Phenol, in particular, is one of several dangerous synthetic compounds created by humans. There were more than 80,000 chemicals produced in the US for industrial use, and many of these are phenol and phenolic compounds that end up in the environment without being subjected to adequate safety assessment. There are several types of bacteria that may use phenol as a carbon source, making bioremediation of this dangerous material a promising possibility. We found that at very high concentrations of phenol, the growth rate of Pseudomonas putida NAUN-16 was significantly slowed down. The primary growth model modified Gompertz was utilized to obtain the growth parameter specific growth rate. In this study, we continue the work by further modelling the effect of substrate or phenol on the growth rate of the bacterium using several substrate inhibition kinetic models such as Monod, Haldane, Teissier, Aiba, Yano and Koga, Han and Levenspiel, Luong, Moser, Webb and Hinshelwood. The resultant fittings show appreciable fitting with the exception of the Monod model. The Teissier model, as opposed to the more widely used Haldane model, better suited the growth rate data at different concentrations of phenol as judged by the results of the RMSE, AICc, adjustedR2, F-test, and bias and accuracy factor. The designated values of the Teissier constants were maximal reduction rate, half saturation constant for maximal reduction and half inhibition constant which are symbolized by max, Ks and Ki were 0.150 1/hr (95% confidence interval 0.120 to 0.180), 162.19 mg/L (95% C.I.55.58 to 268.79) and 1291.94 mg/L (95% C.I. 1067.24 to 1516.65), respectively. The value generated from curve fitting interpolation should not be taken as the actual value and it should be warned of this as the true mumax should be where the gradient for the slope is zero and in this case the value was approximately 0.097 1/h at 385 mg/L phenol.

Heterotrophic ammonium assimilation: An important driving force for aerobic denitrification of Rhodococcus erythropolis strain Y10

Studies on microbial ammonium removal have focused on the heterotrophic nitrification of microorganisms and have rarely studied the role of ammonium assimilation. In this study, Rhodococcus erythropolis strain Y10 with the capacity of aerobic denitrification was screened from the surface flow constructed wetlands that treat high-strength ammonium swine wastewater. Instead of through nitrification, this strain removed ammonium through heterotrophic ammonium assimilation, with the removal rate of 9.69 mg/L/h. The KEGG nitrogen metabolism pathway analysis combined with nitrogen balance calculation manifested that the removal of nitrate and nitrite by R. erythropolis Y10 was achieved through two pathways: 1) assimilation reduction to biomass nitrogen and 2) aerobic denitrification reduction to gaseous nitrogen. Ammonium addition improved the aerobic denitrification rate of nitrate and nitrite. The maximal reduction rates of nitrate and nitrite increased from 7.82 and 7.23 mg/L/h to 9.09 and 8.09 mg/L/h respectively, when 100 mg/L ammonium was separately added to 150 mg/L nitrate and nitrite. Furthermore, the removal efficiency of total nitrogen increased from 69.80% and 77.65% to 89.19% and 91.88%, respectively. Heterotrophic ammonium assimilation promoted the aerobic denitrification efficiency of Rhodococcus erythropolis strain Y10.

Modelling the Inhibition Kinetics of Molybdenum Reduction by the Molybdate-reducing Enterobacter cloacae

The mathematical simulation of physical, chemical or biological data can assist a researcher in explaining the physicochemical or biological phenomenon by predicting or estimating the possible actions, to replicate a prediction or retroactivity and to schedule better experiments. Bacteria are an emerging instrument for the bioremediation of the molybdenum pollutant in the world, molybdenum reduction into insoluble molybdenum blue. In this study, the molybdenum reduction rate by the bacterium Enterobacter cloacae was studied for its inhibitory kinetics characteristics using sodium molybdate as a substrate. Modeling kinetics showed that molybdenum reduction could be explained by several models such as Monod, Haldane, Hans-Levenspiel, Luong, Teissier, Aiba and Yano with Aiba as the best model as judged using error function analysis such as bias and accuracy factors (BF and AF), root mean square error (RMSE), adjusted coefficient of determination (adjR2), and corrected Akaike Information Criterion (AICc). The calculated value for the Teissier-Edward’s constants, which are qmax, Ks, and Ki that are maximal reduction rate, half saturation constant for maximal reduction, half saturation constant for inhibition of reduction were 7.77 (95% C.I., 4.41 to 19.95) mole Mo-blue hr-1, 26.63 (95% C.I., 12.82 to 40.44) mM and 51.39 (95% C.I., 23.67 to 79.10) mM, respectively. The true maximal reduction rate, which occurred when the slope of the curve is zero occurs at 36 mM molybdate concentration and a corresponding value of 1.85 mole Mo-blue hr-1. The fitting parameters of the Monod model prove a strong bacterial resistance to higher toxic molybdenum levels, making the bacterium useful tool for metals bioremediation work.

Modelling the Kinetics Molybdenum Reduction Rate by Morganella sp.

Simulation of physical, chemical or biological data by mathematical approach can aid the researcher explain the physicochemical or biochemical phenomenon. Mathematical models can also be utilized to estimate or predict the possible actions, to replicate a prediction or retroactivity and to schedule better experiments. Bacteria are an emerging instrument for the bioremediation of the molybdenum pollutant in the world, molybdenum reduction into insoluble molybdenum blue. In this study, the molybdenum reduction rate by the bacterium Morganella sp. was studied for its inhibitory kinetics characteristics using sodium molybdate as a substrate. Modeling kinetics showed that molybdenum reduction could be explained by several models such as Monod, Haldane, Hans-Levenspiel, Luong, Teissier, Aiba and Yano with Aiba as the best model as judged using error function analysis such as bias and accuracy factors (BF and AF), root mean square error (RMSE), adjusted coefficient of determination (adjR2), and corrected Akaike Information Criterion (AICc). The calculated value for the Teissier-Edward’s constants, which are qmax, Ks, and Ki that are maximal reduction rate, half saturation constant for maximal reduction, half saturation constant for inhibition of reduction were 7.77 (95% C.I., 4.41 to 19.95) µmol Mo-blue hr-1, 26.63 (95% C.I., 12.82 to 40.44) mM and 51.39 (95% C.I., 23.67 to 79.10) mM, respectively. The true maximal reduction rate, which occurred when the slope of the curve is zero occurs at 36 mM molybdate concentration and a corresponding value of 1.85 µmol Mo-blue hr-1. The model parameters obtained revealed that Morganella sp. have strong resistance to higher toxic molybdenum levels indicating the usefulness of this bacterium for bioremediation.

Preparation of nanofibrillated cellulose from grapefruit peel and its application as fat substitute in ice cream

Grapefruit peel nanofibrillated cellulose (GNFC) was used as fat substitute in ice cream. GNFC was characterized by TEM, SEM, and XRD. The effects of GNFC on textural profiles, rheological properties, melting resistance, sensory properties, microstructure, and gross energy (GE) of ice cream were investigated. The results showed that GNFC was short rod-shaped crystal. Ice cream added with GNFC exhibited elastic-dominated behavior and better textural properties. The sensory evaluation score reached the highest level with desirable three-dimensional network structure at 0.4 % GNFC addition. GE of ice cream significantly decreased with reducing fat with maximal reduction rate of 17.90 %. Furthermore, the results of in vitro simulated digestion showed that GNFC addition and fat reduction significantly inhibited fat digestibility of ice cream due to coalescence of fat droplets on GNFC. This study provides new sustainable perspectives for the application of GNFC prepared from agricultural waste as fat substitute in food products.

Spatial-temporal potential exposure risk analytics and urban sustainability impacts related to COVID-19 mitigation: A perspective from car mobility behaviour

Coronavirus disease-2019 (COVID-19) poses a significant threat to the population and urban sustainability worldwide. The surge mitigation is complicated and associates many factors, including the pandemic status, policy, socioeconomics and resident behaviours. Modelling and analytics with spatial-temporal big urban data are required to assist the mitigation of the pandemic. This study proposes a novel perspective to analyse the spatial-temporal potential exposure risk of residents by capturing human behaviours based on spatial-temporal car park availability data. Near real-time data from 1,904 residential car parks in Singapore, a classical megacity, are collected to analyse car mobility and its spatial-temporal heat map. The implementation of the circuit breaker, a COVID-19 measure, in Singapore has reduced the mobility and heat (daily frequency of mobility) significantly at about 30.0%. It contributes to a 44.3%–55.4% reduction in the transportation-related air emissions under two scenarios of travelling distance reductions. Urban sustainability impacts in both environment and economy are discussed. The spatial-temporal potential exposure risk mapping with space-time interactions is further investigated via an extended Bayesian spatial-temporal regression model. The maximal reduction rate of the defined potential exposure risk lowers to 37.6% by comparison with its peak value. The big data analytics of changes in car mobility behaviour and the resultant potential exposure risks can provide insights to assist in (a) designing a flexible circuit breaker exit strategy, (b) precise management via identifying and tracing hotspots on the mobility heat map, and (c) making timely decisions by fitting curves dynamically in different phases of COVID-19 mitigation. The proposed method has the potential to be used by decision-makers worldwide with available data to make flexible regulations and planning.

Soil particle-size distribution and aggregate stability of new reconstructed purple soil affected by soil erosion in overland flow

Artificial soil erosion caused by engineering practices is becoming increasingly severe worldwide. However, little is known about the change of soil structure of new reconstructed purple soil after erosion in the hilly areas of Southwest China. This study aims to analyze the effects of erosion on the soil particle-size distribution (PSD) and aggregate stability of new reconstructed purple soil in the overland flow under different flow discharges, slope lengths, and slope positions. A series of field scouring experiments was conducted. Flow discharges of 5, 15, and 30 L/min were applied in the new reconstructed purple soil plots with different slope lengths (5, 10, 20, 30, 40, and 50 m). Sediment samples were collected in 550-mL bottles. Soil sampling was conducted from the 0–10-cm layers before and after the field scouring experiments. In the laboratory, the pipette method was used to measure the soil PSD and microaggregates. The macroaggregates were determined by the dry and wet sieving method. Silt particles were eroded most at 30 L/min, by 2.11%. The average maximal reduction rate of the mean weight diameter of soil aggregates (MWD) was 20.23% at 15 L/min. Clay loss was maximal at 1.04%, and the average maximal increasing rate of the > 0.25 mm percentage of aggregate disruption (PAD0.25) was 0.86% at 5 L/min. The silt and MWD maximally decreased by 7.72% and 1.86%, and the maximal sand and PAD0.25 increased by 16.70% and 25.18%, which were all observed in the 10-m plot. The percentage of soil aggregates destroyed by the change in the MWD was − 14.32% on the upslope. Silt sediment showed an increasing rate of 6.36% and microaggregate destruction showed a decreasing rate of 13.00% on the middle slope. Microaggregates and clay particles were mainly deposited on the lower slope and the reduction rates of the silt and sand content were smaller than those on the middle slope. The effects of erosion on the soil PSD and aggregate stability of new reconstructed purple soil in the overland flow under different flow discharges, slope lengths, and slope positions were obviously different. Soil and water conservation measures should be effectively implemented on the upper slope and a slope length of 10-m soil. The soil PSD and MWD could be used as parameters for prediction of soil erosion on new reconstructed purple soil.

Mechanistic Understanding of Predatory Bacteria-Induced Biolysis for Waste Sludge Dewaterability Improvement

Due to the dramatically increasing production of excess sludge during biological wastewater treatment, the development of an economical, efficient, and environmentally friendly sludge dewatering method is highly required. Herein, Bdellovibrio-and-like organisms (BALOs), a group of predatory bacteria were applied for waste sludge dewaterability enhancement and biomass reduction and the potential biolysis mechanisms were elaborated. Generally, the satisfying biolysis performance was obtained for the sludge with the moderate total solid (TS) content (1.5–2.5%). Within 24-h sludge biolysis with our isolated and enriched BALOs, the sludge specific resistance to filtration value as the dewaterbility index reached the maximal reduction rate of 65.3 ± 6.4%. Meanwhile, the concentrations of released soluble nitrogen and phosphorous significantly increased by 57.4 ± 3.3 and 56.7 ± 6.1%, respectively. Moreover, the contents of tightly bound extracellular polymeric substances (EPS) dramatically decreased after sludge biolysis while the loosely bound EPS contents increased, which implied the disruptions of sludge flocs structure for sludge dewaterability improvement. High-throughput sequencing results revealed the remarkable shift of sludge’s microbial community structure after biolysis treatment. The relative abundances of the dominant genera Ferruginibacter, Pseudomonas, and Thermomonas related to denitrification or flocs structure stabilization dramatically decreased. The noticeable increasing populations of Comamonas and Hyphomicrobium in abundances suggested the potential re-growth of the surviving microbial cells in response to BALO invasions. Overall, BALO predation could disintegrate the waste sludge structure, promote the cell lysis and the intracellular substances release, and cause the variations of microbial community compositions to efficiently improve the sludge dewaterability.

Negative lusitropic property of nifekalant identified using ventricular pressure-volume loop analyses in anesthetized monkeys.

The present study was conducted to clarify multiple cardiohemodynamic and electrophysiological properties including inotropic/lusitropic effects of nifekalant, a class III antiarrhythmic drug, in an isoflurane-anesthetized monkey. Nifekalant was administered intravenously at the therapeutic dose of 0.3 mg/kg over 10 min to male cynomolgus monkeys (n=4), followed by higher dose of 1 (n=3) or 3 mg/kg (n=1) that was limited due to arrythmogenicity. Left ventricular (LV) pressure-volume (PV) analysis revealed that the 0.3 mg/kg dose of nifekalant induced a negative lusitropic effect, recognized as a decrease in maximal rate of reduction in LV pressure and a prolonged isovolumic relaxation time. Nifekalant also decreased heart rate and increased LV end-diastolic pressure, but had no effects on the other cardiohemodynamic parameters examined. Electrophysiological analysis showed nifekalant at 0.3 mg/kg prolonged QT/QTc intervals with no evidence of arrhythmia. Higher doses of nifekalant induced ventricular arrhythmia in 3 out of 4 animals, in which both the short-term and long-term variability of the QT interval increased just before the occurrence of arrhythmia. In conclusion, a therapeutic dose of nifekalant had no effect on inotropic activity or cardiac compliance, whereas it showed negative lusitropic properties and QT/QTc prolongation in isoflurane-anesthetized monkeys. In addition, higher doses of nifekalant showed remarkable QT/QTc prolongation leading to arrhythmogenicity, which showed good accordance with clinical findings. Caution should be paid to negative lusitropic properties as well as arrhythmogenisity for the safe use of nifekalant.

Statistical Evaluation of the Mathematical Modelling on the Molybdenum Reduction Kinetics of a Molybdenum-reducing Bacterium

Molybdenum is a global pollutant that has been increasingly found to be toxic tospermatogenesis in several animal model studies. Thus its removal and the studies of its reduction kinetics for removal are very important. In a previous study (1), three kinetic models; i.e. Haldane, Luong and Monod were evaluated to study the reduction kinetics of the molybdenum-reducing bacterium Bacillus sp. strain A.rzi. We revisited the model used in this bacterium and extend the study by incorporating more reduction kinetics models such as Hans- Levenspiel, Yano, Aiba, Webb, Hinshelwood and Teissier. We then evaluated the accuracy of the fitted model using statistical analysis. The best model was Han Levenspiel instead of Luong as proposed previously with the majority of the statistical evaluation such as the lowest values for RMSE, the highest adjusted R2 values and with Bias Factor and Accuracy Factor nearest to unity (1.0) indicated that the model was the best. The calculated values for the Han-Levenspiel constants qmax (the maximum specific substrate reduction rate (h−1), Sm (the critical inhibitor concentration (mM) above which reactions stops), Ks (concentration of substrate giving half maximal reduction rate (mM) and the empirical constants m and n (both dimensionless) were 3.832, 106.16, 48.19, -1.271 and 1.001, respectively. The true qmax value where the gradient forthe slope is zero was 1.107 h-1 at 38 mM molybdate as a substrate. The results indicate that the exhaustive use of mathematical models provides new understanding of the way molybdenum inhibits production into molybdenum blue in bacterium. This can provide new knowledge on ways to predict progress of molybdenum reduction in the laboratory and during bioremediation works.

Should I Stay or Should I Go? The Role of Actuarial Reduction Rates in Individual Retirement Planning in Germany

This paper provides a two-part empirical analysis on how actuarial reduction rates for early retirement affect current pension payments in Germany and to what extent the existence and the magnitude of such reduction rates influence people’s retirement planning. First, when looking at administrative records, early retirement shows a high prevalence at the extensive and at the intensive margin, in particular for women and medium income insurant. Second, a special question in the 2011 SAVE survey is exploited where respondents are offered a hypothetical deal for early retirement if in turn they are willing to accept an actuarial reduction on their pension. It becomes evident that the maximal reduction rate people would be willing to accept is widely dispersed and on average roughly double the current legal rate. Furthermore, respondents seem to make consistent choices and high endowment of financial assets and additional old age provision, high subjective life expectancy, bad health as well as being a man are positively correlated to the actuarial reduction rate the respondents would accept at most. Given that policymakers aim to increase the average retirement age, the results emphasize the need for a simultaneous increase of not only the statutory retirement age but the minimum early retirement age as well, since actuarial reduction rates cannot be expected to change the retirement behavior of workers with a strong preference for early retirement or those who rely on social benefits.

Influence of lactic acid bacteria on the oxidation–reduction potential of buckwheat (Fagopyrum esculentum Moench) sourdoughs

The influence of lactic acid bacteria (LAB) growth on oxidation–reduction potential (ORP) of buckwheat sourdoughs was investigated. Sourdough fermentations are widely used for the production of bread and other bakery products. Until now the pH value is the most used control parameter taken into account during sourdough technology and no information is available about the influence of sourdough microbiota on the ORP or the use of redox potential (Eh7) measurements as a fermentation control parameter. The influence of growth and metabolism of lactobacilli on the oxidation–reduction potential of buckwheat (Fagopyrum esculentum Moench) sourdoughs was investigated. Upon inoculation with LAB, ORP changes were observed. Each strain exhibits a different ORP time course curve. The Eh7 after 8 h using Lactobacillus plantarum, Lactobacillus sakei, Weissella cibaria and Pediococcus pentosaceus reached 89.2 ± 4, 104.5 ± 15.3, 30.2 ± 4 and 181.5 ± 2.6 mV, respectively. W. cibaria showed the highest reducing activity and P. pentosaceus the lowest one. The maximal reduction rate was neither correlated with the highest acidification rate nor with the maximal growth rate. Nevertheless, the reduction rate shows a similar trend like the acidification rate during the time course of fermentation. The ORP changes occurred concomitantly with the acidification, and the acid production decreased after 2 h from the reducing step. These results showed the possibility to carry out ORP measurements in dough system. As strains exhibit very characteristic ORP curves, this parameter can be used as real-time control tool to monitor the time course of fermentation and metabolic activity. This enables an evidence-based determination of fermentation end and/or (intermediate) harvesting point, which is especially helpful in the development of new cereal fermentation types as in gluten-free sourdoughs.

NAD(P)H:quinone oxidoreductase 1 (NQO1) activity threshold in intact pulmonary arterial endothelial cells (PAEC)

One pulmonary endothelial metabolic function is reduction of blood borne redox compounds via NQO1, wherein phase II enzyme induction is a potential means to optimize this function. However, a threshold above which increases in NQO1 activity do not support increases in NQO1 substrate toxicity is seen in other cell types. The goal of this study was to use a kinetic approach to evaluate whether PAEC also exhibit an NQO1 activity threshold. PAEC NQO1 activity in cell cytosol fraction was induced ~6 fold (46.2±3.4 vs 268.1±28.5 nmol/min/mg protein) by exposure to sulforaphane (5 μM;24 hr). However, when intact cell NQO1 activity was measured by addition of duroquinone (DQ; 0‐50 μM) to the extracellular medium, the maximal reduction rate was only ~3 fold higher in sulforaphane than control cells (10.0±0.6 vs 32.2±1.3 nmol/min/mg protein). The possibility that NADPH availability was limiting NQO1 activity in sulforaphane exposed cells was suggested by the observation that glucose‐6‐phosphate dehydrogenase was induced only 1.2 fold (19.6 ± 1.2 vs 23.9 ± 1.6 nmol/min/mg protein). The study demonstrates a threshold effect for intact PAEC NQO1 activity and implies that the pulmonary endothelial NQO1 capacity to activate blood borne anticancer drugs or detoxify xenobiotics is limited by factors other than enzyme activity measured in cytosol fractions. Support: HL‐65537 and Dept. of Veterans Affairs.

Shewanella oneidensis MR-1 Uses Overlapping Pathways for Iron Reduction at a Distance and by Direct Contact under Conditions Relevant for Biofilms

We developed a new method to measure iron reduction at a distance based on depositing Fe(III) (hydr)oxide within nanoporous glass beads. In this "Fe-bead" system, Shewanella oneidensis reduces at least 86.5% of the iron in the absence of direct contact. Biofilm formation accompanies Fe-bead reduction and is observable both macro- and microscopically. Fe-bead reduction is catalyzed by live cells adapted to anaerobic conditions, and maximal reduction rates require sustained protein synthesis. The amount of reactive ferric iron in the Fe-bead system is available in excess such that the rate of Fe-bead reduction is directly proportional to cell density; i.e., it is diffusion limited. Addition of either lysates prepared from anaerobic cells or exogenous electron shuttles stimulates Fe-bead reduction by S. oneidensis, but iron chelators or additional Fe(II) do not. Neither dissolved Fe(III) nor electron shuttling activity was detected in culture supernatants, implying that the mediator is retained within the biofilm matrix. Strains with mutations in omcB or mtrB show about 50% of the wild-type levels of reduction, while a cymA mutant shows less than 20% of the wild-type levels of reduction and a menF mutant shows insignificant reduction. The Fe-bead reduction defect of the menF mutant can be restored by addition of menaquinone, but menaquinone itself cannot stimulate Fe-bead reduction. Because the menF gene encodes the first committed step of menaquinone biosynthesis, no intermediates of the menaquinone biosynthetic pathway are used as diffusible mediators by this organism to promote iron reduction at a distance. CymA and menaquinone are required for both direct and indirect mineral reduction, whereas MtrB and OmcB contribute to but are not absolutely required for iron reduction at a distance.

Kinetic, spectroscopic and thermodynamic characterization of the Mycobacterium tuberculosis adrenodoxin reductase homologue FprA

The genome sequence of the pathogenic bacterium Mycobacterium tuberculosis revealed numerous cytochrome P450 enzymes, which require accessory redox enzymes for catalytic function (ferredoxin reductase and ferredoxin). The most likely ferredoxin reductase is encoded by fprA, and its structure resembles eukaryotic adrenodoxin reductases. We have cloned, expressed and purified the flavoenzyme product of the fprA gene in Escherichia coli. FprA reduces various electron acceptors using either NADPH or NADH as the electron donor, but discriminates in favour of NADPH (apparent K (m) for NADH=50.6+/-3.1 microM; NADPH=4.1+/-0.3 microM from ferricyanide reduction experiments). Stopped-flow studies of reduction of the FprA FAD by NADPH demonstrate increased flavin reduction rate at low NADPH concentration (<200 microM), consistent with the presence of a second, kinetically distinct and inhibitory, pyridine nucleotide-binding site, similar to that identified in human cytochrome P450 reductase [Gutierrez, Lian, Wolf, Scrutton and Roberts (2001) Biochemistry 40, 1964-1975]. Flavin reduction by NADH is slower than with NADPH and displays hyperbolic dependence on NADH concentration [maximal reduction rate ( k (red))=25.4+/-0.7 s(-1), apparent K (d)=42.9+/-4.6 microM]. Flavin reoxidation by molecular oxygen is more rapid for NADH-reduced enzyme. Reductive titrations show that the enzyme forms a species with spectral characteristics typical of a neutral (blue) FAD semiquinone only on reduction with NADPH, consistent with EPR studies. The second order dependence of semiquinone formation on the concentration of FprA indicates a disproportionation reaction involving oxidized and two-electron-reduced FprA. Titration of FprA with dithionite converts oxidized FAD into the hydroquinone form; the flavin semiquinone is not populated under these conditions. The midpoint reduction potential for the two electron couple is -235+/-5 mV (versus the normal hydrogen electrode), similar to that for adrenodoxin reductase (-274 mV). Our data provide a thermodynamic and transient kinetic framework for catalysis by FprA, and complement recent spectrophotometric and steady-state studies of the enzyme [Fischer, Raimondi, Aliverti and Zanetti (2002) Eur. J. Biochem. 269, 3005-3013].

NADH:Fe(III)-chelate reductase of maize roots is an active cytochrome b5 reductase

Microsomal NADH:Fe(III)-chelate reductase (NFR) of maize roots has been purified as a monomeric flavoprotein of 32 kDa with non-covalently bound FAD. In the presence of NADH, NFR efficiently reduced the physiological iron-chelate Fe(III)-citrate ( K cat/ K m(Fe(III)-citrate)=6.0×10 6 M −1 s −1) with a sequential reaction mechanism. Purified NFR was totally inhibited by the sulfhydryl reagent PHMB at 10 −9 M, and it could use cyt b 5 as alternative electron acceptor with a maximal reduction rate as high as with Fe(III)-citrate. We conclude that in maize roots the reduction of Fe(III)-citrate is chiefly performed by a cytochrome b 5 reductase, mostly associated with intracellular membranes and in part with the plasma membrane.

The effects of pH and cations on the spectral and kinetic properties of methylamine dehydrogenase from Thiobacillus versutus.

The catalytic parameters of Thiobacillus versutus methylamine dehydrogenase (MADH) with the physiological substrates methylamine and amicyanin show a pH profile that is quite different from the one found in commonly used assays with artificial electron acceptors. The optimum at pH 7.5, observed for kcat in the latter case, is absent with amicyanin as the reoxidizing substrate. With amicyanin kcat scarcely depends on pH; the same is true for the maximal rate of reduction of MADH by methylamine (kred). Conversely, both the specificity constant (kcat/Km) of MADH for amicyanin and the apparent second-order rate constant for the reduction of MADH by methylamine (kassocapp) increase very sharply with pH. MADH has a high- and a low-affinity binding site for monovalent cations. Cation binding to the high-affinity site, which only binds the larger cations (Cs+, Rb+, and NH4+), is accompanied by a red shift in the absorbance spectrum, whereas cation binding to the low-affinity site, which, less specifically, favors binding of the smaller cations, leads to a bleaching of the visible spectrum with a concomitant increase in the near-UV. Cation binding to either site strongly affects the reactivity of MADH. The reduction of MADH by methylamine is inhibited by monovalent cations, whereas the oxidation of reduced MADH by amicyanin is strongly stimulated. For the former reaction it was established that cations affect only kassocapp, not kred. Some speculations about the molecular basis for the effects of pH and cations are presented.

Follow-up study of combination treatment (TAE and PEIT) for unresectable hepatocellular carcinoma.

The subjects were 35 patients with unresectable hepatocellular carcinoma. The patients were divided into a transcatheter arterial embolization group (TAE group, 18 cases) and a combination therapy group receiving both TAE and percutaneous ethanol injection therapy (TAE+PEIT group, 17 cases). The 50% survival period was 21.1 months for the TAE group and 37.8 months for the TAE+PEIT group (P < 0.05). The longest survival period in the TAE group was 89 months. In the TAE+PEIT group, one patient has survived for 59 months. The actuarial 1-, 2-, and 3-year survival rates for the TAE group were 82%, 45%, and 22%, respectively. For the TAE+PEIT group the rates were 83%, 64%, and 64%, respectively. The TAE+PEIT group showed a significantly higher survival rate in the 895- to 1,074-day period as compared with the TAE group (P < 0.05). Overall, the survival rate tended to be higher in the TAE-PEIT group (P < 0.1). The therapeutic responses of tumors were measured by the maximal reduction rate within 6 months of TAE and PEIT. In the TAE group, a PR was seen in only four cases. In the TAE+PEIT group, CRs and PRs were achieved significantly more frequently than in the TAE group. When the patients were divided into a responder group (CR, PR, and MR) and a nonresponder group (NC and PD), survival was significantly longer in the responder group. The findings of the present study suggest that the combination therapy was useful for improving the survival of patients with unresectable hepatocellular carcinoma.