Peak Specific Activity Research Articles

Self-Supported 3D PtPdCu Nanowires Networks for Superior Glucose Electro-Oxidation Performance.

The development of non-enzymatic and highly active electrocatalysts for glucose oxidation with excellent durability for blood glucose sensors has aroused widespread concern. In this work, we report a fast, simple, and low-cost NaBH4 reduction method for preparing ultrafine ternary PtPdCu alloy nanowires (NWs) with a 3D network nanostructure. The PtPdCu NWs catalyst presents significant efficiency for glucose oxidation-reduction (GOR), reaching an oxidative peak-specific activity of 0.69 mA/cm2, 2.6 times that of the Pt/C catalyst (0.27 mA/cm2). Further reaction mechanism investigations show that the NWs have better conductivity and smaller electron transfer resistance. Density functional theory (DFT) calculations reveal that the alloying effect of PtPdCu could effectively enhance the adsorption energy of glucose and reduce the activation energy of GOR. The obtained NWs also show excellent stability over 3600 s through a chronoamperometry test. These self-supported ultrafine PtPdCu NWs with 3D networks provide a new functional material for building blood glucose sensors and direct glucose fuel cells.

The Sedimentation Rate in the Crimean Hypersaline Lake Aktashskoye Estimated Using the Post-Chernobyl Artificial Radionuclide 90Sr as a Radiotracer

Artificial 90Sr is one of the most important long-lived radionuclides of global radioactive fallout from the atmosphere after the testing of nuclear weapons and the accident at the Chernobyl Nuclear Power Plant in 1986. In addition to fallout from the atmosphere, secondary radioactive contamination of Crimea was mainly from the Dnieper River and the North Crimean Canal, which occurred until 2014. 90Sr was used as the optimal radiotracer for estimating the rate of sedimentation in the Crimean hypersaline lake. Its vertical distribution in the bottom sediments was assessed. In the core of the bottom sediments, the detectable activity of 90Sr in layers 0–1.5 cm and 16.7–21.9 cm was absent, and it was determined again in the layer of 15.5 cm, which was associated with atmospheric fallout of the radionuclide after the Chernobyl NPP accident. There were well-isolated peaks of specific activity in layers at a depth of 4.6 and 13.3–14.3 cm. The calculated rate of sedimentation varied within 0.5–1.5 cm year−1: the minimum rate corresponded to the period 1971–2017, and the highest rate corresponded to the period 1954–1971.

Defective Layered Double Hydroxide Nanosheet Boosts Electrocatalytic Hydrodechlorination Reaction on Supported Palladium Nanoparticles

Electrocatalytic hydrodechlorination on Pd, utilizing the H+ of H2O as hydrogen sources, represents a promising technology to detoxify the chlorinated organic pollutants (COPs) in water bodies. However, Pd alone affords limited activity due to its low efficacy in H2O disassociation and the poor mass diffusion of COPs that are commonly of low concentrations in the environment. Herein, we demonstrate that arming Pd with OH– vacancy-bearing NiAl-layered double hydroxide nanosheets (Pd/NixAl100–x-LDH-OHv) can significantly improve its performance, benefiting from the enhanced H2O disassociation at OHv and the facilitated C–Cl cleavage on the supported Pd nanoparticles. Al3+ is also indispensable because it promotes the formation and regeneration of OHv, but an overload will reduce the number of accessible OHv and weaken its function. Pd/Ni67Al33-LDH-OHv with the optimal Ni/Al ratio delivers a peak specific activity of 0.53 min–1 m–2 and mass activity of 6.54 min–1 g–1Pd in treating 50.0 mg L–1 2,4-dichlorophenol (2,4-DCP, a probe COP) at −0.25 V versus RHE, outperforming most of the reported catalysts. To address the mass diffusion issue, Pd/Ni67Al33-LDH-OHv is integrated into a customized continuous-flow membrane cell. When fed a dilute wastewater (20.4 mg L–1), the system affords a 2,4-DCP removal rate of 3.75 g2,4-DCP gcatalyst–1 h–1 and faradaic current efficiency of 42.6%, which is 3.2 and 4.0 times that obtained in a traditional batch reaction system, respectively.

Optimizing the metal-support interactions at the Pd-polymer carbon nitride Mott-Schottky heterojunction interface for an enhanced electrocatalytic hydrodechlorination reaction

We reported one novel strategy via band engineering of the semiconductor support to optimize the metal-support interactions at a Mott-Schottky heterojunction interface and enhance the metal’s electrocatalytic hydrodechlorination (EHDC) performance. Taking palladium-polymer carbon nitride (Pd/PCN) as a model, the band tuning of PCN by heteroatomic phosphorus (P) doping substantially boosted the EHDC of 2,4-dichlorophenol (2,4-DCP, one typical chlorinated organic pollutants (COPs)) on Pd, and a peak specific activity of 0.172 min−1 cmPd−2 was achieved by Pd/P-PCN-0.25 (0.25 reflected the P content, and denoted the mass ratio of the P source to PCN precursor used in P-PCN synthesis), quadrupling 0.041 min−1 cmPd−2 of Pd/C and outperforming most of the reported catalysts. The mechanism study revealed the P doping in PCN enabled the positive shift of its Fermi level, which weakened the Pd-PCN interactions and alleviated the electron excess of Pd in Pd/PCN. The P-PCN in Pd/P-PCN-0.25 with the ideal band structure evoked a Pd electronic state that maximized EHDC efficiency. Further investigation into the intermediate products of EHDC on Pd/P-PCN and the biological safety of the 2,4-DCP-contaminated water after EHDC treatment demonstrated the EHDC over our catalyst was environmental-benignity for COPs abatement.

Developmental changes in physiological amino acids and hepatic methionine remethylation enzyme activities in E10‐21 chick embryos and D1‐49 broilers

The remethylation of homocysteine to methionine is important for chick embryos to sustain the S-adenosylmethionine transmethylation reactions, which are essential for the rapid proliferation of cells. Developmental changes in hepatic 5-methyltetrahydrofolate-homocysteine methyltransferase (MFMT), betaine-homocysteine methyltransferase (BHMT) and hepatic serine hydroxymethyltransferase (SHMT) were determined in E10-21 Cobb 500 broiler chick embryos and hatched chicks from D1-49. Hepatic levels of free serine, glycine, putrescine, spermidine and spermine levels were also determined. Analyses showed hepatic MFMT-specific activity doubled from E10 to E12, with remaining embryo development experiencing small fluctuations in activity through E21. Hepatic MFMT doubled immediately after hatch, with peak activity occurring at D3. Afterwards, hepatic MFMT-specific activity steadily declined from D7-49. Hepatic BHMT activity was higher from E10 to E16 of embryogenesis, decreased rapidly at E17 and remained lower through E21 (p<.05). Hepatic BHMT-specific activity was also lower in chicks, with the exception of a peak in specific activity on D7. BHMT activity returned to lower levels by D21. Throughout embryogenesis, hepatic SHMT activity in chick embryos remained relatively constant except for a decrease at 13E, followed by an increase at 14E. Maximal activity of SHMT was found the first day post-hatch. Additionally, SHMT activity was significantly lower in growing chicks than that in embryos. Hepatic-free serine and glycine levels were negatively correlated with SHMT in hatched chicks. Hepatic polyamine, putrescine and spermidine shared a similar development pattern: peak level in the middle of incubation, low at late embryogenesis and lowest during the post-hatch period except an increase within one week after hatch. The sharp increase in hepatic concentrations of glycine, serine and putrescine, along with increased specific activities of MHMT, BHMT and SHMT from D1-7, suggests that methionine conservation (remethylation from homocysteine) and glycine/serine is critical for young chicks for organ growth, maturation, and development.

Nanoporous gyroid platinum with high catalytic activity from block copolymer templates via electroless plating

Nanoporous platinum (Pt) with a gyroid nanostructure was fabricated using a nanoporous polymer with gyroid nanochannels as a template. The nanoporous polymer template was obtained from the self-assembly of the degradable block copolymer, polystyrene-b-poly(L-lactide) (PS-PLLA), followed by the hydrolysis of the PLLA blocks. Templated electroless plating can be conducted under ambient conditions to create a precisely controlled Pt gyroid nanostructure with high crystallinity in a PS matrix. After removal of the PS matrix, the well-interconnected nanoporous gyroid Pt can be successfully fabricated. Compared with commercially available catalysts, the nanoporous Pt possesses superior macroscopic stability and peak specific activity, benefiting from the well-defined network structure with robust texture and the growth of the low-index crystalline facets of Pt.

Kinetic study of phenol hydroxylase and catechol 1,2-dioxygenase biosynthesis by Candida tropicalis cells grown on different phenolic substrates

When Candida tropicalis was grown on phenol, catechol or resorcinol, the highest levels of specific activity of phenol hydroxylase (EC. 1.14.13.7) and catechol 1,2-dioxygenase (EC. 1.13.11.1) were attained with phenol. With the three aromatic compounds tested, the yeast cells exhibited sharp peaks of specific activity of both enzymes at particular incubation times. Phenol-induced cells containing high levels of both enzymes were capable of degrading rapidly and without delay 4-chlorophenol and 2,6-dichlorophenol, and to a lesser extend pentachlorophenol. However, the yeast could not grow on chlorophenols as major carbon and energy source.

Increased fibroblast growth factor-like autoantibodies in serum from a subset of patients with cancer-associated hypercalcemia

Basic fibroblast growth factor (bFGF) is a potent tumor angiogenesis factor which lacks an amino-terminal signal sequence and does not normally circulate in serum from normal subjects. Naturally-occurring autoantibodies which mimicked basic fibroblast growth factor were described in serum from patients with multiple endocrine neoplasia type 1 prolactinoma or sporadic growth-hormone-secreting adenoma associated with increased bFGF. Since bFGF was increased in serum from a variety of cancers, we used endothelial cell proliferation assay(s) to test for bioactivity in the IgG fraction of serum from 56 patients with cancer-associated hypercalcemia, and normal or control subjects. We now report increased IgG-like endothelial cell activity in serum from a hyper prolactinemic subset (4/19 breast cancer; 1/14 renal cancer; 0/23 lung cancer) of cancer-associated hypercalcemic subjects. Highest activity was found in serum from three breast cancer patients who suffered spinal cord compression/metastases. The activity had properties of antiidiotype bFGF antibodies including reaction with anti-human IgG antibodies, and complete neutralization by rabbit antibodies to intact bFGF. The activity in endothelial cells persisted after storage at 0–4 C for 5 yrs; and [prepared by SDS-PAGE and immunoblotting with anti-human IgG] had apparent mol wt corresponding to the heavy chains of IgG. Serum IgG-like activity from 5 of 5 breast cancer patients and 2 of 2 prostate cancer subjects tested [prepared by anti-bFGF antibody, protein-A immunoaffinity, and hydroxyapatite (HA) chromatography] yielded peak HA-adsorbed activity that eluted with 0.4 M sodium phosphate, and was neutralized 70% by antibodies to intact bFGF. Cancer sera mean peak specific activity (12.0 ng-eq bFGF/ug protein) (n = 7) significantly exceeded (P < 0.001) normal sera mean peak specific activity (0.46 ng-eq bFGF/ug protein) (n = 6) in the 0.4 M sodium phosphate eluate fraction from hydroxyapatite columns. These results imply that long-lasting, bioactive FGF-like autoantibodies may arise spontaneously (and contribute to pathophysiology) in subsets of cancer patients with osseous metastases.

The assembly of hepatic very low density lipoproteins: evidence of a role for the Golgi apparatus.

Previous studies from our laboratory have suggested that the assembly of lipoproteins by the liver is not completed in the rough endoplasmic reticulum but continues while the particles are en route to or within the Golgi apparatus. To investigate further the role of the Golgi apparatus in lipoprotein assembly, mice were injected with [3H]glycerol and killed 7.5 to 45 min after injection. Microsomes and Golgi apparatus-rich fractions were isolated from the livers and separated into membrane and content fractions. TG within microsomal and Golgi membranes were labeled, rapidly reaching peak specific activity within 7.5 min of isotope injection. The specific activity of TG in microsomal membranes decreased to approximately 40% of peak values by 45 min, whereas the specific activity of TG in the Golgi membranes decreased to approximately 30% of peak values by 45 min. To determine whether the turnover of the Golgi membrane TG pool was dependent on microsomal TG transfer protein (MTP), mice were gavaged with an MTP inhibitor, and the labeling experiments were repeated. Inhibition of MTP attenuated the turnover of newly synthesized Golgi membrane TG by approximately 50% and the turnover of microsomal membrane TG by approximately 40%. Based on the rapid turnover of the Golgi membrane TG pool and the attenuation of the turnover of this pool by MTP inhibitor, we propose that lipid is transferred from the Golgi membrane to luminal lipoproteins in an MTP-dependent manner. The results support our hypothesis that assembly of VLDL continues within the Golgi apparatus.

Purification and some properties of pectinesterase from potato (Solanum tuberosum L.) alpha cultivar

Pectinesterase was extracted from potato alpha cultivar, purified and partially characterized The used protocol resulted in a 58.8-fold purification (51 850.2 units/mg protein) with 15.5% recovery of pectinesterase activity. The purified enzyme had a molecular weight of 27 kDa and its isoelectric point was around 4.5 with pH and temperature optima of 8.0 and 60°C, respectively. The purified enzyme had a single symmetric peak of specific activity after chromatographic steps. The homogeneity of the purified pectinesterase was confirmed by gel filtration and polyacrylamide electrophoresis gel.

Tissue-specific changes in the activities of antioxidant enzymes during the development of the chicken embryo

1. Tissue-specific profiles of the expression of the antioxidant enzymes superoxide dismutase (SOD), glutathione peroxidase (GSH-Px) and catalase (CAT) and the concentrations of reduced glutathione (GSH) during the development of the chick embryo were investigated. 2. The liver, brain, yolk sac membrane (YSM), kidney, lung, heart and skeletal muscles were collected at the following days of embryo development: 10, 11, 13, 15, 17, 19, 21 and 22 (day-old chicks). 3. The different tissues of the embryo displayed distinct development strategies with regard to the acquisition of antioxidant capacity. In the liver the specific activity of SOD increased between days 10 and 11 of development, then significantly decreased up to day 15 and remained at the same value during the rest of the developmental period. GSH-Px specific activity increased through the time of development. CAT had 2 peaks of specific activity at day 10 of the development and in day-old chicks. 4. The brain was characterised by comparatively high SOD-specific activity especially during the last days of incubation. The specific activities of GSH-Px and CAT were low throughout development. 5. In the YSM maximal GSH-Px and CAT-specific activities were found on day 15 of incubation. In the kidney and heart GSH-Px-specific activity increased at hatching time. CAT-specific activity in the kidney increased just after hatching. 6. It is concluded that each tissue studied expressed a profile of antioxidant defence mechanisms to deal with oxidative stress at hatching time.

Purification and Characterization of a Complex from Placental Syncytiotrophoblast Microvillous Membranes which Inhibits the Proliferation of Human Umbilical Vein Endothelial Cells

The signs of pre-eclampsia are thought to arise from maternal endothelial dysfunction caused by circulating factors of placental origin. Syncytiotrophoblast microvillous membranes (STBM) cause endothelial disruption and inhibit proliferation in vitro. Significantly increased amounts of STBM can be detected in blood from pre-eclamptic women and could contribute to endothelial dysfunction in vivo. This study purified a complex from STBM which inhibits the proliferation of cultured human endothelial cells. Integral membrane proteins were solubilized with sucrose monolaurate. Anion exchange chromatography yielded two peaks of anti-proliferative activity. Only the second peak was specific to STBM and was subjected to further separation by Sephacryl S-200 gel filtration chromatography (GFC). A single peak of specific activity eluted close to the void volume, at a position unaltered by added denaturing agents, guanidium chloride or urea. On Sephacryl S-300 GFC, two peaks were obtained of 410 and 820kDa, with similar anti-proliferative activity and protein components (by SDS-polyacrylamide gel electrophoresis). The major protein bands were as integrins α5and αv, dipeptidyl peptidase IV, α-actinin, transferrin, transferrin receptor, placental alkaline phosphatase and monoamine oxidase A.

A specialized form of RNA polymerase I, essential for initiation and growth-dependent regulation of rRNA synthesis, is disrupted during transcription.

Only a small proportion (<2%) of RNA polymerase I (pol I) from whole-cell extracts appeared to be competent for specific initiation at the ribosomal gene promoter in a yeast reconstituted transcription system. Initiation-competent pol I molecules were found exclusively in salt-resistant complexes that contain the pol I-specific initiation factor Rrn3p. Levels of initiation-competent complexes in extracts were independent of total Rrn3p content and varied with the growth state of the cells. Although extracts from stationary phase cells contained substantial amounts of Rrn3p and pol I, they lacked the pol I-Rrn3p complex and were inactive in promoter-dependent transcription. Activity was restored by adding purified pol I-Rrn3p complex to extracts from stationary phase cells. The pol I-Rrn3p complex dissociated during transcription and lost its capacity for subsequent reinitiation in vitro, suggesting a stoichiometric rather than a catalytic activity in initiation. We propose that the formation and disruption of the pol I-Rrn3p complex reflects a molecular switch for regulating rRNA synthesis and its growth rate-dependent regulation.

Over-expression and characterization of active recombinant rat liver carnitine palmitoyltransferase II using baculovirus

The cDNA encoding rat liver carnitine palmitoyltransferase II (CPT-II) was heterologously expressed using a recombinant baculovirus/insect cell system. Unlike Escherichia coli, the baculovirus-infected insect cells expressed mostly soluble active recombinant CPT-II (rCPT-II). CPT activity from crude lysates of recombinant baculovirus-infected insect cells was maximal between 50 and 72 h post-infection, with a peak specific activity of 100-200 times that found in the mock- or wild-type-infected control lysates. Milligram quantities (up to 1.8 mg/l of culture) of active rCPT-II were chromatographically purified from large-scale cultures of insect cells infected with the recombinant baculovirus. The rCPT-II was found to be: (1) similar in size to the native rat liver enzyme (approximately 70 kDa) as judged by SDS/PAGE; (2) immunoreactive with a polyclonal serum raised against rat liver CPT-II; and (3) not glycosylated. Kinetic analysis of soluble rCPT-II revealed Km values for carnitine and palmitoyl-CoA of 950 +/- 27 microM and 34 +/- 5.6 microM respectively.

Intracellular Sorting of Lysosomal β-Glucuronidase Is Altered Due to Administaration of Dibutyl Phosphate1

Organophosphate compounds are known to cause a selective increase of beta-glucuronidase activity in rat serum. Previous data suggested that increase of serum beta-glucuronidase activity was well correlated with decrease of that activity in rat liver microsomal fraction, thereby, suggesting a role of the microsomal enzyme in mediating the organophosphate effect. To investigate further the intracellular sorting pathway of beta-glucuronidase in dibutyl phosphate-treated rats, liver subcellular fractions were prepared at 12 or 48 h after in vivo administration of [3H]leucine and it was established that microsomal beta-glucuronidase was the origin of the increased serum enzyme. To characterize the intracellular secretory pathway of beta-glucuronidase in dibutyl phosphate-treated rats, Golgi subfractions were isolated and a time course study was carried out. At 30 min after administration of dibutyl phosphate, specific activity of beta-glucuronidase in GF-2 (Golgi intermediate fraction) and GF-3 (Golgi heavy fraction) was significantly increased to the maximum. Furthermore, colchicine pretreatment of rats caused a delay of the peak of specific activity for 30 min in GF-2 and GF-3, and accumulation of enzyme activity in Golgi subfractions was observed. Colchicine pretreatment also had an inhibitory effect on release of beta-glucuronidase into serum until 30 min after dibutyl phosphate injection. The electrophoretic pattern of microsomal beta-glucuronidase on polyacrylamide gel was found to show two major bands of microsomal enzyme type and lysosomal enzyme type in dibutyl phosphate-treated rats. Taken together, these findings indicate that microsomal beta-glucuronidase follows the intracellular secretory pathway and is secreted into serum via Golgi complex in response to dibutyl phosphate.

Ontogenetic development of digestive enzyme activities in larval walleye pollock, Theragra chalcogramma

Activities of digestive enzymes trypsin, amylase and lipase in laboratory-reared walleye pollock, Theragra chalcogramma, were measured from hatching to Day 39 (just before notochord flexion) in 1993. All measurements were conducted individually or semi-individually (groups of two larvae of the same standard length). Close relationships between digestive enzyme activities and morphological development of digestive organs were observed. Activities of trypsin and lipase were low during the transition period from endogenous to exogenous energy. Amylase activity was constant with large variance during the same period. Specific enzyme activities of trypsin and amylase indicated high values with large variance during the early period. All three enzyme activities increased with age afterthe transition period, and the specific enzyme activities became constant. The existence of two types of lipase was suggested. One lipase showed a peak of specific activity at Day 4 and might be related to yolk-sac absorption. The activity of the other lipase increased with age after Day 14 and might be related to digestion of prey lipid. Our results suggest that digestive enzymes included in food organisms supplement larval pollock digestive enzymes.

Cell wall hydrolytic enzyme activity during development of nonclimacteric sweet cherry (Prunus aviumL.) fruit

SummaryThe cell wall hydrolytic enzyme activities of polygalacturonase (PG, EC 3.2.1.15), pectinmethylesterase (PME, EC 3.1.1.11) and carboxymethylcellulase (Cx-cellulase, EC 3.2.1.4) were detected during development of nonclimacteric sweet cherry (Prunus avium L. ‘Bing’) fruit in 1992. Peak specific activity of all three hydrolytic enzymes occurred when fruit was red, 65 d after anthesis. Total protein content of fruit decreased from the earliest green coloured stage, 34 d after anthesis, until the later red-coloured stage, then increased to a maximum in mature, dark-red fruit, 74 d after anthesis. Thus, the highest enzyme activities on a tissue fresh weight basis occurred in dark-red fruit. Fruit firmness declined significantly after endocarp lignification (‘pit hardening’), 45 d after anthesis, and, therefore, was inversely related with increases in PG, PME and Cx-cellulase activities. Two in situ applications of 20 mg 1−1 gibberellic acid (GA3) decreased the activities of PG and PME and increased frui...

Microstructural Effects on Electrocatalytic Oxygen Reduction Activity of Nano‐Grained Thin‐film Platinum in Acid Media

The oxygen reduction activity of thin‐film platinum deposits on carbon and its relationship to catalyst microstructure has been investigated using rotating‐disk‐electrode techniques. The thin‐film form of platinum is a viable tool for catalyst study as it can provide intrinsic activity data on finely divided carbon‐supported platinum. Sputtered polycrystalline thin‐film platinum deposits on carbon (loading from 6 to 200 μg/cm2) have been characterized, and their oxygen reduction activity at 25°C in 1M sulfuric acid determined. Catalyst characterization consisted of electrochemical surface‐area measurement and establishing grain size, morphology, and lattice parameter using transmission electron microscopy. Thin‐film platinum exhibits a reduced lattice parameter at very small grain size. Mass activity and specific activity at 0.9 V vs. reversible hydrogen electrode both decrease with increasing grain size (and decreasing specific surface area). Peak mass activity for oxygen reduction was 25 A/g of Pt, and peak specific activity was 0.070 mA/cm2 of Pt surface. The activity trends are attributed to the changes in electronic and geometric properties.

Transport of 22:6n-3 in the Plasma and Uptake into Retinal Pigment Epithelium and Retina

Vertebrate retina is highly enriched in 22-carbon polyunsaturated fatty acids (PUFAs), especially docosahexaenoic acid (DHA, 22:6n-3), which is supplied by the plasma. To study the transport and uptake of 22:6n-3 into the retina, young Long Evans rats were fasted overnight and given an oral dose of palm oil containing [4,5- 3H] 22:6n-3 and [9,10- 3H] 18:1n-9 (oleic acid). At 1, 6, 12, 24, and 48 hr postgavage, blood, liver, retinal pigment epithelium (RPE) and retina were collected, and plasma lipoprotein fractions were obtained by density-gradient ultracentrifugation. The distribution of radioactivity among the different lipoproteins (dpm%) showed that both fatty acids were mainly associated with VLDL 1 hr after gavage. For 22:6n-3, the majority of radioactivity was associated with LDL at 6 hr postgavage. By 12 hr post administration, the majority of radioactivity was in HDL 2 which retained around 40% until the 48-hr time point. For 18:1n-9, a different profile was observed. By 6 hr postgavage, approximately 30% of the radioactivity was found in HDL 2, but the percentage of radioactivity decreased to approximately 20% thereafter. The haft-life of 22:6n-3 was significantly longer than for 18:1n-9 ( P < 0·0005) in plasma, liver, and the lipoprotein fractions. The specific activities of 22:6n-3 and 18:1n-9 in the plasma continuously declined from 1 hr to 48 hr postgavage, while liver showed a peak of specific activity at 6 hr, then gradually declined. The specific activity of 22:6n-3 peaked at 12 hr in RPE, but continued to increase in ROS for up to 48 hr. Our data suggest that: both 22:6n-3 and 18:1n-9 are transported in the circulation by conventional lipoprotein pathways. After intestinal absorption, they are first associated with VLDL (major amount) and soluble proteins (small amount). They are later incorporated into LDL and subsequently into HDL 2. We also conclude that 22:6n-3 is cleared from the blood more slowly than 18:1n-9, and retinal 22:6n-3 is supplied from circulation through the RPE to the ROS.

Dependence of in vivo inactivation kinetics of gramicidin S synthetase on cell physiology

Gramicidin S synthetase, the enzyme complex catalyzing the biosynthesis of the antibiotic gramicidin S in Bacillus brevis, is subject to O(2)-dependent in vivo inactivation during exponential aerobic growth after reaching a peak in specific activity. The five amino acid substrates of the synthetase are capable of stabilizing its activity to varying degrees in whole cells shaken aerobically. Depending on the time of cell harvesting before, during, or after the peak in intracellular gramicidin S synthetase specific activity, the enzyme has a long, medium, or short half-life, respectively. The kinetic profiles of gramicidin S synthetase in B. brevis cells indicate that both the kinetics of synthetase loss and the degree of its amino-acid-mediated stabilization are a strong function of the cells' physiological development.