PubMed Health⌕ Search

Biomedical subjects

S D Varfolomeev

Publications and source records attributed to S D Varfolomeev.

At least 91 records · Page 5Linked to original sources
PubMed1982

[Inactivation of prostaglandin endoperoxide synthetase from the microsomal fraction of human platelets during the reaction].

The kinetic regularities of the prostaglandin endoperoxide synthetase in human platelets microsomes were studied. It was shown that at low equilibrium of the reaction the reaction product yield linearly depends on the enzyme concentration. The value of the inactivation rate constant is not dependent on the enzyme concentration, is not changed within the pH range of 6-9 and is markedly increased with a rise in hemin concentration. The kinetics of thermoinactivation of the enzyme at 4 degrees and 32 degrees was studied. It was concluded that inactivation occurs via intermediate enzyme-substrate complexes. The enzyme is also inactivated in the presence of hemin and oxygen. The latter process is eliminated in the presence of an electron donor (epinephrine) in a medium.

Blood Platelets↗
PubMed1982

[Enzyme inactivation in the course of the reaction. Kinetic description and discrimination of mechanisms].

The kinetic regularities of the enzymatic reaction involving substrate depletion and enzyme inactivation were studied. Various inactivation mechanism including monomolecular inactivation of the free enzyme or the enzyme--substrate complex and bimolecular inactivation with the substrate and reaction product were investigated. The possibility of discrimination of these mechanisms and determination of the kinetic parameters for these processes based on integral equations are discussed.

Enzyme Inhibitors↗
PubMed1981

[Inhibition mechanism of Polyporus versicolor laccase by halide ions].

A kinetic study of inhibition of Polyporus versicolor laccase activity by fluoride-, chloride- and bromide ions has been carried out. It has been found that the fluoride ion is a non-competitive inhibitor with respect to the electron donor and a mixed inhibitor with respect to oxygen. However, the chloride and bromide ions are competitive inhibitors with respect to the electron donor. The constants of inhibition of the enzyme activity by both chloride and fluoride ions and the catalytic constant were found to be pH-dependent. Based on the pH-dependence of the catalytic constant, an existence of two ionogenic groups in the enzyme active site has been proposed. The existence of an alternative electron pathway in the enzyme active site is postulated. This pathway makes a noticeable contribution to the reaction rate when the concentration of the electron donor and the fluoride ion is high. This alternative electron pathway can be blocked by the chloride ions and the hydroxyl ions taken at high concentrations. A formal kinetic description of this phenomenon has been given and the role of the type 2 Cu2+ in the catalytic process has been evaluated.

Basidiomycota↗
PubMed1980

[Reversible oxidation-reduction of NAD by hydrogen, catalyzed by soluble hydrogenase from Alcaligenes eutrophus Z-1].

The kinetics of NAD reduction by hydrogen, catalyzed by soluble hydrogenase from the hydrogen bacterium A. eutrophus Z-1 within a wide range of NAD substrate concentrations and pH were studied under aerobic and anaerobic conditions. The autocatalytic type of the reaction (with an induction period) and positive kinetic cooperativity with respect to NAD substrate at pH values greater than 8.0 were observed. A steady hydrogen release in a two-enzyme system involving hydrogenase, formiate dehydrogenase, formiate and NAD was demonstrated. A multistep pattern of the reaction mechanism of NAD reduction allowing to explain the autocatalytic type of NAD reduction by hydrogen as well as insensitivity of the reaction to air oxygen were proposed. Possible types of regulation of the soluble hydrogenase activity in the cell are discussed.

Aerobiosis↗
PubMed1979

[Inner and outer immobilization of chloroplasts].

The effects of glutaric aldehyde on pea leave chloroplasts and their inactivation kinetics were studied. Optimization of the chloroplasts fixation by glutaric aldehyde resulted in a 5-fold increase of stability of the chloroplasts. Immobilization of the chloroplasts in agar-agar gels was performed; the ability of chloroplasts for photooxidation of H2O was thereby retained. Immobilization did not actually affect the stability of chloroplasts. The inactivation kinetics of fixed and immobilized chloroplasts are in good agreement with the previously described model for inactivation of native chloroplasts.

Aldehydes↗
PubMed1979

[Isolation, purification and study of the stability of the soluble hydrogenase of Alcaligenes eutrophus Z-1].

Soluble hydrogenase was isolated from the hydrogen-oxidizing bacterium Alcaligenes eutrophus Z-1 and purified to electrophoretical homogeneity. The purification procedure included fractionation by ammonium sulfate, ion-exchange chromatography on DEAE-cellulose and gelfiltration through Ultragel AcA-34. The resulting preparation had a specific activity of 25 mkmoles H2.min-1.mg of protein as measured by the rate of hydrogen evolution from sodium dithionite-reduced methyl viologen. The enzyme has a molecular weight of 200,000 and is made up of two subunits with mol. weights of 30,000 and two subunits with mol. weights of 65,000. The effects of pH, oxidants and reducers, as well as aerobic and anaerobic conditions on the hydrogenase preparations inactivation kinetics in intact cells and in a highly purified state were studied. The kinetic data suggest a possible existence of two enzyme forms differing in their activities and stabilities to denaturating influences.

Air↗
PubMed1978

[Mass-transfer and kinetics of microencapsulated alpha-chymotrypsin action].

A theoretical model for transient and steady-state kinetics of microencapsulated enzymes action has been developed. The model is meant to overcome the diffusional limitations, caused by a microcapsulated membrane. The effects of various parameters (enzymatic reaction rate constants, enzyme concentration in microcapsules, membrane permeability, substrate concentration, and bulk pH values) on the overall apparent reaction rate have been analyzed using esters hydrolysis catalyzed by alpha-chymotrypsin encapsulated into polycarbonate membranes as an example.

Carbonates↗
PubMed1977

[Relationships of photoreduction of substituted salts of 4,4'-dipyridyl by isolated chloroplasts].

Kinetic relationships of photoreduction of 4,4'-dimethyldipyridyl and 4,4'-dibenzyldipyridyl in the presence of chlorplast were studied. It was found that photoreduction leads to the establishment of photosteady state in which the rate of photoreduction is equal to the rate of dark oxidation of reduced form. Kinetics of dark oxidation of photoreduced form were investigated. The study of inhibition of photoreduction of methylviologen and potassium ferricyanide by diuron was performed. It was shown that the nature of inhibition of both reactions is completely identical. The effect of hydrogen ions concentration and gas phase composition was studied. Stabilization of low potential electron acceptors to the oxidation by molecular oxygen in the reaction of photooxidation of water is discussed.

Chloroplasts↗
PubMedDate not supplied

[Fibrinolytic and fibrinogenolytic effects of acyl urokinase and urokinase combinations in vitro].

The in vitro thrombolytic and side effects of double-strand urokinase-type plasminogen activator (tcu-PA), p-guanidinobenzoyl tcu-PA (GB-tcu-PA), and their combinations were compared. The reversible blocking of the active site stabilizes GB-tcu-PA in human plasma and results in longer thrombolysis and lesser side effects than those of tcu-PA. However, the acylated activator displays a marked lag period of thrombolytic action. GB-tcu-PA and tcu-PA combinations (molar ratios 4 : 1 and 1 : 1) induce a prolonged and effective thrombolysis without the initial lag period at a low level of plasminogen, fibrinogen, and alpha2-antiplasmin depletion in the plasma surrounding the clot.

Enzyme Stability↗