Search results for "Kinetic"
showing 10 items of 3064 documents
Isolation of a Putative Hydroxyacyl Enzyme Intermediate of an Epoxide Hydrolase
1994
A putative covalent, alpha-hydroxyacyl intermediate was isolated by the brief exposure of murine soluble epoxide hydrolase to its substrate. The reaction was reversed by time and blocked by competitive inhibitors. The formation of the intermediate was dependent upon the concentration of the enzyme and was increased by incubation under acidic conditions. The structure of the intermediate was supported by microchemical methods.
Properties and amino acid composition of pure epoxide hydratase
1975
1. Introduction Rat liver epoxide hydratase [EC 4.2.1.631 which catalyses the conversion of epoxides to trurans-dihydro- diols has been purified to apparent homogeneity as determined by three independent criteria [l] . The preparation obtained was capable of catalysing the hydration of both styrene oxide and the 4,5- (K- region)epoxide of benzo(a)pyrene [ 11. Epoxides of polycyclic hydrocarbons have been implicated as the agents responsible for the cytotoxic and carcinogenic properties of such compounds (for reviews see [2-41). A detailed knowledge of the properties of epoxide hydratase may, therefore, contribute towards an understanding of the mechanisms of cytotoxicity and carcinogenesis.…
Influence of the level of cytosolic epoxide hydrolase on the induction of sister chromatid exchanges by trans-beta-ethylstyrene 7,8-oxide in human ly…
1991
Abstract trans -β-Ethylstyrene 7,8-oxide, a substrate of cytosolic epoxide hydrolase, and 4-fluorochalcone oxide, an inhibitor of this enzyme, were investigated on induction of sister chromatid exchanges (SCE) in human lymphocytes. Both epoxides enhanced the frequency of SCE. 4-Fluorochalcone oxide at low concentration (2.5μM) inhibited cytosolic epoxide hydrolase activity towards trans -β-ethylstyrene 7,8-oxide in lymphocytes by 74% and had no effect on glutathione transferase activity using this substrate. At this concentration it did not induce SCE itself, but it potentiated the effect of trans -β-ethylstyrene 7,8-oxide several fold. In lymphocytes from different subjects, the number of …
Naturally occurring hemolysins in the coelomic fluid of Holothuria polii delle chiaie (Echinodermata).
1979
Abstract The coelomic fluid of Holothuria polii D.Ch contains hemolytic activity against erythrocytes of several vertebrate species. The hemolytic potency depends upon calcium ion concentration and varies according to erythrocyte source and cell number in the reaction mixture. Absorption experiments with formalinized rabbit erythrocytes suggest that hemolytic activity is not specific. Its heat lability, water insolubility at low pH values, and sensitivity to proteolytic enzymes suggest that hemolytic activity resides in protein molecules. The activity, maximal in alkaline media, appears to depend up time and temperature.
An easy-to-use model for O2 supply to red muscle. Validity of assumptions, sensitivity to errors in data
1995
An easy-to-use capillary cylinder model of O2 supply to muscle is presented that considers all those factors that are known to be most important for realistic results: (1) red blood cell (RBC) O2 unloading along the capillary, (2) effects of the particulate nature of blood, (3) free and hemoglobin-facilitated O2 diffusion and reaction kinetics inside RBCs, (4) free and myoglobin-facilitated O2 diffusion inside the muscle cell, and (5) carrier-free region separating RBC and tissue. In a first approach, a highly simplified yet reasonably accurate treatment of the complex three-dimensional oxygen diffusion field in and next to capillaries is employed. As an alternative, a more realistic descri…
A preliminary study on the distribution of morphine and its glucuronides in the subcompartments of blood.
1998
[Abstract ] The distribution of morphine, morphine-3-glucuronide (M3G), and morphine-6-glucuronide (M6G) in whole blood, plasma, and packed erythrocytes was studied. Parameters investigated were the hematocrit values (10, 42, 44, and 71%) and the water content of the samples. The blood-to-plasma ratio of morphine concentrations was unaffected by variations in hematocrit and water content, whereas the corresponding ratios for M3G and M6G were strongly influenced. Ratios were 0.53 to 0.65 and 0.52 to 0.62 in specimens with average hematocrit values (42 and 44%, respectively), and the ratios were 0.81 or 0.89 (hematocrit 10%) and 0.27 or 0.28 (hemalocrit 71%) in blood samples with different he…
Hemoglobin dynamics in rat erythrocytes investigated by M�ssbauer spectroscopy
1991
Rats have been enriched in 57Fe and erythrocytes were isolated from the blood. Mössbauer absorption spectroscopy on the hemoglobin of these erythrocytes has shown rather similar dynamics as found earlier in crystals of myoglobin, in frozen solutions of human hemoglobin and in a number of other proteins. The results strongly indicate that the motion of the heme and presumably some part of the F-helix is mainly influenced by the average viscosity of the sample determined by a network of hydrogen bridges and other weak interactions. Extrapolations of Mössbauer results from protein crystals to proteins in their physiological surroundings seem to be suitable for heme proteins.
Involvement of carboxyl groups in chloride transport and reversible DIDS binding to band 3 protein in human erythrocytes
2011
AbstractNoncovalent DIDS binding to Band 3 (AE1) protein in human erythrocyte membranes, modified by non-penetrating, water soluble 1-ethyl-3-(4-azonia-4,4-dimethylpentyl)-carbodiimide iodide (EAC), was studied at 0°C in the presence of 165 mM KCl. Under experimental conditions applied up to (48 ± 5) % of irreversible chloride self-exchange inhibition was observed. The apparent dissociation constant, KD, for “DIDS-Band 3” complex, determined from the chloride transport experiments, was (34 ± 3) nM and (80 ± 12) nM for control and EAC-treated resealed ghosts, respectively. The inhibition constant, Ki, for DIDS was (35 ± 6) nM and (60 ± 8) nM in control and EAC-treated ghosts, respectively. T…
Oligomerization and hemolytic properties of the C-terminal domain of pyolysin, a cholesterol-dependent cytolysin
2013
Pyolysin (PLO) belongs to the homologous family of the cholesterol- dependent cytolysins (CDCs), which bind to cell membranes containing cholesterol to form oligomeric pores of large size. The CDC monomer structure consists of 4 domains. Among these, the C-terminal domain 4 has been implicated in membrane binding of the monomer, while the subsequent processes of oligomerization and membrane insertion have primarily been assigned to other domains of the molecule. Recombinantly expressed or proteolytic fragments that span domain 4 of the CDCs streptolysin O and perfringolysin O bind to membranes but fail to oligomerize, and they inhibit the activity of the respective wild-type toxins. We repo…
Enzymes involved in the dynamic equilibrium of core histone acetylation ofPhysarum polycephalum
1992
DEAE-Scpharose chromatography of extracts from plasmodia of the myxomyccte PI~.~suru~~t ,~/.~crpl~~ho~~ revealed the presence of multiple histone acetyltransferases and histonc deacctylascs. A cyloplasmic histonc acctyltransferase B, specific for histonc H4, and two nuclear acetyltransferases Al and A2 were identilied; Al acetylates all core hislones with a preference for l-13 and H2A. whereas A2 is specific for H3 and also slightly for H2B. Two hislone deacetylases. HDI and HD2, could be discriminated. They differ with respect to subslralc speciliciiy and pH dependence. For the first time the substrate specificity of histonc deacetylascs was determined using HPLC-purilicd individual core h…