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Biomedical subjects

A I Archakov

Publications and source records attributed to A I Archakov.

At least 127 records · Page 7Linked to original sources
PubMed1985

Influence of cholesterol and prostaglandin E1 on the molecular organization of phospholipids in the erythrocyte membrane. A fluorescent polarization study with lipid-specific probes.

Anthryl-labeled fluorescent probes closely mimicking phosphatidylcholine and sphingomyelin were applied to study the state of these phospholipids in the rabbit erythrocyte membrane. At normal cholesterol levels both probes exhibited higher fluorescence polarization values in the membranes than in phospholipid vesicles of similar lipid composition, indicating a decreased fluidity of the probe environment in erythrocyte ghosts. In ghosts prepared from normal erythrocytes no evidence of lateral separation of phosphatidylcholine and sphingomyelin was found. At higher cholesterol levels, however, these lipids appear to segregate. Probably the effect of cholesterol on the erythrocyte membrane lipids involves lipid-protein interactions. At physiological concentrations, prostaglandin E1 only weakly affects the state of phosphatidylcholine and sphingomyelin in erythrocyte membranes. Cholesterol enrichment amplifies the effect of prostaglandin E1. Although the prostaglandin E1-induced changes depended much upon whether the ghosts were enriched with cholesterol in vitro or in vivo, with both types of ghosts effects of prostaglandin E1 were seen at extremely low effector concentrations that may have presented a few molecules of prostaglandin per ghost. The structural and functional significance of these findings is discussed.

Alprostadil↗
PubMed1985

[Inactivation of cytochrome P-450 in hydroxylase reactions].

It has been shown that sodium azide, a catalase inhibitor, accelerates the inactivation of cytochrome P-450 in reactions of hydroxylation of type I substrates, e.g., dimethylaniline (DMA), aminopyrine (AP), benzphetamine (BPh), p-nitroanisole (p-Na) and type II substrates--aniline (AN). In the absence of sodium azide, cytochrome P-450 is either non-activated (as in the case of AN) or is inactivated at a low rate. Haemoprotein inactivation in the presence of sodium azide in all hydroxylation reactions with the exception of O-demethylation of p-NA is a first-order reaction with respect to cytochrome P-450. Studies on the mechanism of cytochrome P-450 inactivation demonstrated that hydrogen peroxide formed via the NADPH-dependent hydroxylase cycle exhibits an inactivating effect towards the enzyme. The value of inactivation constant for cytochrome P-450 in hydroxylation reactions proceeding in the presence of sodium azide coincides with that of enzyme inactivation in the NADPH-oxidase and glucose oxidase systems generating H2O2.

Animals↗
PubMed1985

[Stoichiometry of microsomal oxidation reactions. Distribution of redox-equivalents in monooxygenase and oxidase reactions catalyzed by cytochrome P-450].

The stoichiometry of NADPH oxidation in rabbit liver microsomes was studied. It was shown that in uncoupled reactions cytochrome P-450, besides O2- generation catalyzes direct two- and four-electron reduction of O2 to produce H2O2 and water, respectively. With an increase in pH and ionic strength, the amount of O2 reduced via an one-electron route increases at the expense of the two-electron reaction. In parallel, with a rise in pH the steady-state concentration of the oxy-complex of cytochrome P-450 increases, while the synergism of NADPH and NADH action in the H2O2 formation reaction is replaced by competition. The four-electron reduction is markedly accelerated and becomes the main pathway of O2 reduction in the presence of a pseudo-substrate--perfluorohexane. Treatment of rabbit with phenobarbital, which induces the cytochrome P-450 isozyme specific to benzphetamine results in a 2-fold increase in the degree of coupling of NADPH and benzphetamine oxidation. The experimental results suggest that the ratio of reactions of one- and two-electron reduction of O2 is controlled by the ratio of rates of one- and two-electron reduction of cytochrome P-450. In the presence of pseudo-substrates cytochrome P-450 acts predominantly as a four-electron oxidase; one of possible reasons for the uncoupling of microsomal monooxygenase reactions is the multiplicity of cytochrome P-450 isozymes.

Aniline Hydroxylase↗
PubMed1984

[Change in the properties of plasma membranes of normal and neoplastic cells after incorporation of cholesterol].

It is shown that cholesterol incorporation into the membranes of lymphocytes, lymphoblast leikose cells L1210 and into those of ovary tumor causes an increase in the membrane phospholipid bilayer microviscosity measured by pyrene as a fluorescent probe. An increase in the membrane lipid microviscosity resulted in a decrease in the activity of Na+, K+-ATPase and 51-nucleotidase of the normal and tumor cells. After the injection of the tumor cells with an elevated cholesterol/phospholipid ratio an increase of the life span in the experimental animals as compared with the control group was observed.

5'-Nucleotidase↗
PubMed1983

The influence of cholesterol incorporation and removal on lipid-bilayer viscosity and electron transfer in rat-liver microsomes.

The incorporation and removal of cholesterol from rat liver microsomes was used as a methodical approach to investigate the molecular organization of microsomal redox-chains. It was shown that the incorporation of cholesterol in microsomes increases and removal of cholesterol decreases lipid bilayer viscosity as indicated from the rate of fluorescent probe-pyrene eximerisation in cholesterol-enriched and cholesterol-depleted microsomes. The increase of membrane viscosity slows down the initial rates and decreases the rate constants of cytochrome b5 reduction by NAD(P)H, whereas the decrease of membrane viscosity enhances the initial rates and increases the rate constants of these reactions. The rates of cytochrome P450 reduction by reduced pyridine nucleotides do not depend on the viscosity of lipid bilayer. The incorporation and removal of cholesterol from microsomes was not followed by any essential changes in the rates of dimethylaniline N-demethylation, aniline p-hydroxylation, p-nitroanisole O-demethylation, oxygen consumption, oxidation of NADH and NADPH. Thus the reduction of cytochrome b5 by NADH and NADPH is the diffusion-dependent reaction in the redox-chains of microsomes only.

Animals↗
PubMed1983

[Conformational state and functional activity of NADPH-dependent cytochrome P-450 reductase isolated and incorporated into phospholipid bilayers].

It was shown that the alpha-helix content in both isolated and incorporated into phospholipid bilayer NADPH-dependent cytochrome P-450 reductase is 20%. NADPH or dithionite reduction of the flavoprotein is not followed by conformational changes. The incorporation of the NADPH-dependent cytochrome P-450 reductase molecule into the phospholipid bilayer does not affect its catalytic properties. It was found that the protein does not interact with the phospholipid bilayer of phosphatidyl choline liposomes but incorporates readily into the liposomal membrane from a microsomal phospholipid mixture with a binding constant of 17.4 microM.

Animals↗
PubMed1983

[Effect of cytochrome b5 on the functional activity and conformational state of cytochrome P-450].

Microsomal cytochromes P-450 and b5 were shown to form mixed complexes with the association constant of 0.24 microM in water solution. Such complex formation stabilizes cytochrome P-450 in the catalytically active conformational state characterized by increased conformational rigidity and temperature stability. This stabilization results in acceleration of the cumene hydroperoxide-dependent oxidation of p-nitroanisol catalyzed by cytochrome P-450. The thermodynamic parameters of O-demethylation of p-nitroanisol catalyzed by cytochrome P-450 and mixed haemoprotein complexes measured in water solution and in a membrane-bound state were found to be different.

Cytochrome P-450 Enzyme System↗
PubMed1983

[Comparative inhibitory analysis of aniline hydroxylation by cytochrome P-450 in NADPH-, hydroperoxide cumyl- and H2O2-dependent systems].

The p-hydroxylation of aniline in the presence of liver microsomes and isolated cytochrome P-450 in NADPH-, H2O2- and cumyl hydroperoxide (CHP)-dependent systems was investigated. A comparative inhibitory analysis of these reactions was carried out. It was shown that the mechanism of the H2O2-dependent hydroxylation reactions is similar to that of the NADPH-dependent monooxygenase reactions and, consequently, this model system should be preferably used for the study of the mechanisms of aniline hydroxylation reactions instead of the CHP-dependent system. Since the kcat value for the H2O2-dependent system is much higher than that for the NADPH- or CHP-systems, it may be assumed that when H2O2 is used as a cosubstrate for this reaction, the true value of the degradation constant for the cytochrome P-450--O2(2-)--aniline peroxycomplex can be measured.

Aniline Hydroxylase↗
PubMed1983

[Effect of antitubercular preparations on the isoform composition of cytochrome P-450 of rat liver microsomes].

The effects of the antituberculous drugs, isoniazide, phthivazide, streptomycin and PAS, on the isoform content of rat liver microsomal cytochrome P-450 was studied by electrophoresis in acrylamide concentration gradient (5-15%) in the presence of sodium dodecyl sulphate. It was discovered that administration of the antituberculous drugs did not increase the specific content of cytochrome P-450 in rat liver microsomes. At the same time isoniazide had an inducing effect on isoforms of cytochrome P-450, with molecular weights of subunits varying within the range of 49000 to 50000 dalton. Phthivazide induced subfractions with molecular weights of subunits being equal to 50000, 49000 and 47500 dalton. PAS induced subfractions with molecular weights of subunits being equal to 54000, 50000, 49000, and 47500 dalton. Administration of streptomycin did not affect the isoform content of rat liver microsomal cytochrome P-450. For comparison purposes, a study was made of the generally recognized cytochrome P-450 inductors, phenobarbital and 3-methylcholanthrene. It is suggested that the changes in the isoform content of rat liver microsomal cytochrome P-450 might be of importance for understanding the mechanism of drug tolerance induction in the treatment of tuberculosis, since the changes discovered are likely to lead to the increased metabolic rate of the antituberculous drugs at the cytochrome P-450 level and to the accelerated excretion from the body.

Animals↗
PubMed1982

[Rapid transmembrane migration of phosphatidylcholine under the influence of cytochrome P-450].

The phosphatidylcholine exchange protein and bee venom phospholipase A2 were used to estimate the phosphatidylcholine accessibility in proteoliposome-containing cytochrome P-450. Without cytochrome P-450 phosphatidylcholine was only partly accessible for the both membrane probes. Incorporation of cytochrome P-450 into the liposomes resulted in a complete accessibility of phosphatidylcholine for the phosphatidylcholine exchange protein and phospholipase A2. On the other hand, phosphatidylcholine was only partly available for the membrane probes in cytochrome b5 containing proteoliposomes. It was concluded that cytochrome P-450 induces rapid transmembrane translocation of phosphatidylcholine with tau 1/2 less than 20 min. It is proposed that cytochrome P-450 may be responsible for rapid flip-flop of phosphatidylcholine in rat liver microsomes.

Androgen-Binding Protein↗
PubMed1982

[Sorption decholesterolization of the blood].

Results of haemosorption with the use of activated carbon IGI in patients with different diseases of the liver are given. It is shown that along with the toxic metabolites the method serves to remove a considerable quantity of cholesterol. It is surmised that haemosorption can become an effective method of control of hypercholesterolemia in atherosclerosis and its complications. The results of stand tests of sorbents specific for cholesterol are presented. A sorbent, synthesized from a metal-containing polymer was used for haemosorption in experiments on rabbits with alimentary hypercholesterolemia. Single haemosorption lasting 30 min led to a two-fold decrease of the cholesterol level in the blood and to a two-fold decrease of the damaged area in the aorta 4 weeks after operation.

Animals↗