PubMed Health⌕ Search

Biomedical subjects

L M Vaĭner

Publications and source records attributed to L M Vaĭner.

At least 19 recordsLinked to original sources
PubMed1991

[Quantitative determination and reversible modification of sulfhydryl groups in low and high molecular weight compounds using a biradical spin marker].

A new method for quantitation of sulfhydryl groups of low and high molecular weight compounds is proposed. The method is based on the use of a biradical spin label carrying a disulfide bond, RS-SR, where R is the imidazoline radical. It was found that this biradical is involved in the reaction of thiol-disulfide exchange with thiols; the EPR spectra of the original biradical and monoradical products differ essentially. This circumstance made it possible to determine the bimolecular rate constant for the biradical interaction with cysteamine, cysteine, glutathione and human serum albumin. The method was used for measuring glutathione and cysteine levels in murine and rat blood and for assaying the insect acetylcholine esterase activity and reversible inhibition of NADPH-cytochrome P-450 reductase. The method is marked for a high sensitivity (10(-6)-10(-7) M) towards sulfhydryl groups and allows the determination of thiol groups in coloured and nontransparent solutions.

Acetylcholine↗
PubMed1990

[Macromolecular spin pH-probes on the basis of human serum albumin].

Human serum albumin has been chemically modified by two different spin pH-sensitive labels of the imidazoline series containing in their structure alkylating and carboxyl groups, respectively. The ESR spectra of spin-labeled proteins are sensitive to pH of the medium. The pK values of spin-labeled proteins measured by the ESR method are: pKI = 3.2 +/- 0.1; pKII = 4.75 +/- 0.1. The resulting macromolecular spin pH probes may be used for measuring the local values of pH by the ESR technique within the pH range of 1.8-6.2.

Electron Spin Resonance Spectroscopy↗
PubMed1989

[Affinity modification of membrane-bound microsomal cytochrome P-450 with lipophilic analogs of substrates].

The following lipophilic spin-labeled cytochrome P-450 analogs were synthesized: 2-octyl-4-(3-iodine-2-oxopropylidene)-2,3,5,5-tetramethylimidaz olidine-1-oxyl (RIII), 2-nonyl-4-(3-iodine-2-oxopropylidene)-2,3,5,5-tetramethylimidaz olidine-1-oxyl (RIV), 2-hepta-decyl-4-(3-iodine-2-oxopropylidene)-2,3,5,5-tetramethyl imidazolidine-1- oxyl (RV). The distribution coefficients, k, in water--lipid and water--octanol systems as well as the theoretical estimates of k for these and previously synthesized analogs, i.e., 4-(3-iodine-2-oxo-propylidenyl)-2,2,3,5,5-pentamethylimidazolid ine-1-oxyl (RI) and 2-hexyl-4-(3-iodine-2-oxopropylidene)-2,3,5,5-tetramethylimidaz olidine- 1-oxyl (RII) were determined. It was shown that RIII and RIV bind as type I substrates to cytochrome P-450 from rat microsomes induced with phenobarbital or 3-methylcholanthrene as well as to those from control rats. Radicals RIII and RIV inhibit the oxidation of aniline, aminopyrine and benzphetamine. RIII-RV strongly inhibit the O-deethylation of 7-etoxyresorufin. The inhibitory activity of the radicals increases in the following order: RV less than RIV less than or equal to RI less than or equal to RIII less than RII. The experimental results suggest that the inhibitory properties are nonmonotonuesly related to the lipophility. The high lipophility of RIII and its strong inhibitory properties permit to render the latter to the class of inhibitors which can be transported by liposome membrane vehicles to the liver, inhibit the in vivo activity of the microsomal system and thus prolong the effects of drugs oxidized by cytochrome P-450.

Affinity Labels↗
PubMed1989

[A study of the interaction of substrates with cytochrome P-450 by a method of UV- and 1H-NMR spectroscopy].

Acceleration of substrate longitudinal relaxation (T1) was used to study cytochrome P-450-aminopyrine (1st type substrate) and P-450-4-methoxypyridine (2nd type substrate) complexes. Dissociation constant, T1 and/or residence time of substrate in the complex can be obtained from the dependence of T1 of substrate protons on substrate concentration. Basing on the relaxation times, distances between Fe3+ ion in the active site and protons of the substrate moiety were determined. For aminopyrine all the distances proved to be about 8 A. In the P-450-4-methoxypyridine complex the pyridine nitrogen is directed towards Fe3+ ion. Cytochrome P-450 is compared with its denatured form, cytochrome P-420, and metmyoglobin.

Aminopyrine↗
PubMed1988

[Penetration of ascorbic acid into bilayer phospholipid membranes].

Using the EPR method, the temperature dependencies of the rates of ascorbic acid-induced reduction of nitroxyl radicals carrying the nitroxyl fragment in different positions of the fatty acid chain [N(4-methylidene++-1-oxyl-2,2,5,5-tetramethyl-3-imidazolidine hydrazine)]myristic acid (I) and 1-oxyl-2,2-dimethyloxazolidine derivatives of 5-ketostearic (II) and 12-ketostearic (III) acids incorporated into egg phosphatidylcholine liposomal membranes were studied. The reduction rates, activation energy and shape of kinetic curves were found to be dependent on the mode of liposome preparation (ultrasonication or reverse phase evaporation), label type and chemical composition of the membrane (with regard to the presence or absence of stearic acid). The coefficients of partition and diffusion of ascorbic acid through the membrane lipid bilayer were calculated from the rates of transbilayer (flip-flop) diffusion of I and ascorbate penetration inside the liposomes containing Fremi salt nitroxyl radical. The experimental results formed the basis for a hypothesis on the dependence of the rate of membrane-embedded spin probe reduction on the ascorbate distribution pattern inside the lipid bilayer.

Ascorbic Acid↗
PubMed1987

[Substrate reduction and oxygen activation during microsomal metabolism of quinones].

2-Dimethylamino-3-chloro-1,4-naphthaquinone (DCNQ) was used to study oxygen and substrate activation in microsomal system. DCNQ was shown to be bound to microsomal cytochrome P-450 as a type I substrate; its N-demethylation was catalyzed by cytochrome P-450. Cytochrome P-450 and NADPH-cytochrome P-450 reductase are capable of DCNQ reduction to semi- and hydroquinones. The OH-radical formed in the presence of DCNQ, NADPH and reductase was detected, using a spin trap (5,5-dimethylpyrroline-N-oxide). The OH-radical formation was shown to be stimulated by the Fe-EDTA complex. Using the OH-radical scavengers (mannitol, N-butanol, alpha-naphthol) and the catalase inhibitor sodium azide, it was shown that the OH-radical participates in microsomal oxidation of DCNQ and aminopyrine. It was assumed that in the course of microsomal oxidation the reduced DCNQ is responsible for: i) stimulation of molecular oxygen reduction to H2O2; ii) reduction of Fe ions (Fe3+----Fe2+) which cause the decomposition of H2O2 in the Fenton reaction resulting in the formation of a strong oxidizing agent--a hydroxyl radical.

Animals↗
PubMed1987

[Effect of the lipophilic spin-labeled inhibitor of cytochrome P-450 on the activity of the microsomal system].

It was shown that the lipophilic nitroxyl radical--2-hexyl-2,3,5,5-tetramethyl-4-(3-iodo-2-oxopropyliden)-im idazolidine- 1-oxyl, an affinity modified of rat liver microsomal cytochrome P-450, interacts with various forms of cytochrome P-450 as substrate type I, and it inhibits the oxidation of substrates specific for these forms. During its intravenous injection with egg phosphatidylcholine liposomes the radical is partly bound to liver microsomes, which is accompanied by a decrease of the oxygenase activity of microsomal preparations (by 30-50%) as well as by prolongation of the soporific effect of hexabarbital (2-3-fold).

Animals↗
PubMed1985

[Use of spin-labelled substrate analogs for a comparative study of microsomal cytochrome P-450 and P-448].

The previously described, iodine-labeled alkylating stable nitroxyl radicals located at different distances between the N-O. group and the iodine atom were used for a comparative study of the structure of microsomal cytochromes P-450 and P-448 active centers. The radicals were shown to change the optical spectra of Fe3+ located in the active site of the enzyme that are similar to those induced by cytochrome P-450 substrates. Some differences in the type of the radicals binding to control, phenobarbital- and 3-methylcholanthrene-induced microsomes were revealed. The alkylating radical substrate analogs covalently bound to microsomal cytochrome P-450 in the vicinity of the active center, resulting in the inhibition of oxidation of type I and II substrates (e. g., aniline and naphthalene). The value of the spectral binding constant (Ks) for naphthalene in the presence of the radical covalently bound to the cytochrome P-450 active center showed a tendency to increase. Using the ESR technique, the interaction between Fe3+ and the radical localized in the active site of cytochrome P-450 was demonstrated. The contribution of Fe3+ to the relaxation of the radicals covalently bound to cytochrome P-450 was evaluated from the values of the spin label ESR spectra saturation curves at 77K. The distances between the N-O. group of these radicals and Fe3+ in the enzyme active center for the three types of microsomes were determined. The data obtained point to structural peculiarities of the active center of cytochrome P-450, depending on the microsomal type.

Aniline Compounds↗
PubMed1985

[Inhibition of enzymes of insecticide detoxication in insects by an alkylating analog of a cytochrome P-450 substrate].

It was shown that the alkylating analog of cytochrome P-450 substrate - 4-bromomethyl-2,2,5,5-tetramethyl-3-imidazoline-3-oxide-1-oxyl effectively inhibits in vitro the activities of monooxygenases, glutathione-S-transferases and esterases from the abdomen of the house fly Musca domestica L. The non-alkylating analog (RH) appeared to be a very weak inhibitor of these enzymes. It was demonstrated that the inhibitory action of the alkylating analog consists in its covalent binding to the enzyme protein. Topical application of the cytochrome P-450 alkylating analog on insects led to a decrease of the enzyme activity by approximately 20%.

Animals↗
PubMed1983

[Interactions of microsomal cytochrome P-450 with spin-labeled substrate analogs].

The iodine-containing stable iminoxyl radicals with various distances between the N-O-group and the iodine atom are proposed to be used to study the structure of the active center of the microsomal cytochrome P-450. The radicals used induce changes in the optical spectra of the Fe3+ ion located in the active center of the enzyme, as in the case of type 1 substrates and inhibit essentially the microsomal oxidation of cytochrome P-450 substrates of type 1 and 2. This inhibition is neither due to suppression of the NADPH-cytochrome c reductase activity nor to cytochrome P-450 conversion to cytochrome P-420. Cytochrome P-450 substrates (aminopyrine) protect the enzyme against the radical-induced inactivation. The iodine-containing radicals are covalently bound to cytochrome P-450 in the vicinity of active center. The values of dissociation constants for the reversible enzyme-radical constants and the rate constants for the monomolecular transformation in the complex, k, were determined. The EPR method was used to detect the coupling between Fe3+ and the radical located in the active center of cytochrome P-450. The saturation curves of radical SPR spectra at 77 degrees K were employed to determine the contribution of Fe3+ to the relaxation time, T1, of the radicals covalently bound to cytochrome P-450 and to estimate the distances between the Fe3+ ion and the N-O-group of these radicals in the enzyme active center.

Animals↗
PubMed1982

[Interaction of the Cu(Lys)2 complex with the NADPH-dependent microsomal electron transport system and microsomal membrane].

The low molecular weight analog of superoxide dismutase, th Cu(Lys)2 complex inhibits the oxidation of type I (piperidinoanthraquinone) and type II(aniline) substrates catalyzed by cytochrome P-450. This fact is not associated with the conversion of cytochrome P-450 into the inactive form--cytochrome P-420. It was shown that the method of determining the activity of NADPH-cytochrome c-reductase by the cytochrome c reduction rate cannot be employed in the presence of the Cu(Lys)2 and Cu(Tyr)2 complexes. Potassium ferricyanide was used to demonstrate that Cu(Lys)2 does not affect the NADPH-cytochrome c-reductase activity. The inhibiting effect of Cu(Lys)2 on the microsomal oxidation of the substrates does not result from the interaction of the complex with the components of the NADPH-dependent microsomal electron transport system. The effect observed can be accounted for by the dismutase-like action of the complex on the superoxide radicals generated during the microsomal oxidation of the substrates. The interaction of Cu(Lys)2 with the membrane was studied by the ESR method using stable nitroxide rabicais. It was shown that the complex cannot freely diffuse through the lipid bilayer membrane. A model for Cu(Lys)2 incorporation into the membrane is proposed.

Animals↗
PubMed1979

[Cytochrome P-450 catalyzed oxidation of 1-piperidinoanthraquinone].

Oxidation of 1-piperidinoantraquinone (1-PA) in microsomal fractions of rat liver was studied. The only product of complete oxidation of 1-PA--(N-antraquinone-1)-delta-aminovaleric acid-was identified using paper and thin-layer chromatography. The participation of cytochrome P-450 in oxidation of 1-PA was demonstrated by sharp inhibition, involving blowing of the microsomes with CO and treatment with sodium deoxycholate. Studies of differential spectra of cytochrome P-450 in the presence of 1-PA are indicative of the first type of binding between 1-PA and cytochrome P-450. The binding constants (Ks) and the kinetic parameters (Km and V) for the above substrate in control microsomes and in those induced by phenobarbital and 3-methyl cholanthrene were determined. The results obtained suggest that cytochrome P-450 is involved in oxidation of a number of heterocyclic compounds resulting in the opening of the ring.

Animals↗
PubMedDate not supplied

[The study of the structure of active center of membrane-bound cytochrome p-450 using 1-naphthoxyalcanthiols].

Homologous 1-naphtoxyalcanthiols of the type 1-C10H7O(CH2)nSH (n = 2-7) are used for structural studies of the microsomal cytochrome P450 active centre. It was found that the strongest complex of thiol with P450 is formed for n = 3. Microsomal oxidation of P450 substrates aminopyrine and benz(a) pyrene is inhibited by the 1-naphtoxyalcanthiols studied. A non-monotonous dependence of pI50 on n was found, the compound with a chain length n = 3 appeared to be the most effective inhibitor. The interaction of this thiol (n = 3) with both the heme group of P450 and the hydrophobic substrate zone is supposed and the distance between these points was estimated. It is possible to employ this approach for structural studies on the active centers of different isoforms of P450.

Animals↗
PubMedDate not supplied

[Effect of a magnetic field on the rate of H202 breakdown by catalase and by an Fe3+--EDTA complex].

The acceleration of H202 decomposition induced by catalase and the dimer complex [Fe3+(EDTA)]2 has been observed in a constant magnetic field. The effect increases with the field increasing up to 8000 Oe, reaching 20 +/- 5% and 24 +/- 5% for catalase and [Fe3+(EDTA)]2 respectively. The results are discussed within the hypothesis of a one-electron reaction mechanism using the models developed specially to explain the magnetic effects in radical reactions. It is supposed that the stage which is affected by the magnetic field is the electron transfer coupled with Fe3+O./2 paramagnetic species. The interpretation proposed does not exclude an alternative possibility of the magnetic effects during the electron transfer to two iron atoms by a two-electron (synchronous) mechanism.

Catalase↗
PubMedDate not supplied

[Interaction of RNA polymerase of Escherichia coli with substrate by affinity labeling and NMR with nuclear 31P].

The affinity labeling of E. coli RNA polymerase by periodate oxidized uridine triphosphate was carried out without and with the template (polydeoxynucleotides poly(dA) and poly(dT) ), and under the conditions of poly(dA) and poly(dT) transcription. The extent of RNA polymerase labeling was nearly the same in the presence of poly(dA) and poly(dT) (0.9 and 0.7). However, during the transcription of poly(dA) the extent of RNA polymerase labeling proved to be more than twice as high as that in the case of poly(dT) (0.75 and 0.3). The longitudinal relaxation times (T1) for phosphorus of ATP and dinucleotide pUpU in the complexes of RNA polymerase with the template (poly(dA) and poly(dT) in the presence of MnCl2 were determined. The distance from the phosphorus of enzyme-bound ATP and pUpU and the Mn2+ ion coordinated at the active center on RNA polymerase were calculated using the Solomon - Blombergen formula. According to the results of the affinity labeling of RNA polymerase and the NMR (nuclear magnetic resonance) experiments it can be inferred that the template influences the formation of the working conformation of the enzyme active center, specific with respect to the true substrate, in the stage of RNA elongation.

Affinity Labels↗