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Biomedical subjects

A V Lebedev

Publications and source records attributed to A V Lebedev.

At least 55 records · Page 3Linked to original sources
PubMed1990

[Study of the spatial structure of the duplex d(pTGTTTGGC) d(pCCAAAC)A in aqueous solution by methods of uni- and two-dimensional (1)H-NMR spectroscopy and organic molecular mechanics].

Structure of the complementary complex d(pTGTTTGGC) d(pCCAAAC)A in the aqueous solution has been investigated by one- and two-dimensional 1H NMR spectroscopy. The resonances of nonexchangeable protons of bases as well as methyl and deoxyribose 1', 2'a, 2'b, 3' and 4' protons have been assigned by means of two-dimensional J-correlated spectroscopy (COSY) and two-dimensional nuclear Overhauser enhancement spectroscopy (NOESY). Using one-dimensional NOE measurements, 62 interproton distances (intranucleotide: (H6/H8)i--(H1')t, (H6/H8)i--(H2'a)i, (H1')i--(H2'a)i, (H1')i--(H2'b)i; internucleotide: (H6/H8)i--(H1')i-1, (H6/H8)i--(H2'a)i-1, (H6/H8)i--(H2'b)i-1, (H5/CH3)i--(H6/H8)i-1, (H5/CH3)i--(H2'a/H2'b)i-1) have been determined for nearest-neighbour protons. Spin-coupling constant values for some sugar protons have been obtained from COSY spectra. The restrained molecular mechanics calculations have yielded the possible solution structures of duplex fitting the experimental set of interproton distances and coupling constants.

Base Sequence↗
PubMed1990

[The effect of holotoxin A1 on transport of calcium ions across the lipid models of biological membranes].

Planar bilayer lipid membranes formed from trepang phospholipids possess an intrinsic Ca2(+)-permeability. These phospholipids dissolved in a non-polar solvent can extract 45Ca2+ from the aqueous to the organic phase. The triterpenic glycoside holotoxin A isolated from the trepang Stichopus japonicus inhibits the Ca2+ flux of lipid bilayers from trepang phospholipids as well as the Ca2+ flux induced in phosphatidylcholine bilayers by the calcium ionophore X-537A. Toxin inhibits the Ca2+ ionophore A23187 induced Ca2+ efflux from phosphatidylcholine liposomes and 45Ca2+ transition from the aqueous to the organic phase. Holotoxin A does not inhibit the 45Ca2+ transfer to the non-polar phase induced by holoturia phospholipids and does not affect the phosphatidylcholine hydroperoxide-induced Ca2+ flux of lipid bilayers. Using the fluorescent probe pyrene, it was demonstrated that toxin increases the microviscosity of liposomal membranes and trepang oocyte "ghosts".

Animals↗
PubMed1990

[Clinical course and treatment of traumatic rectal fistula].

From experience in treatment of 104 patients with rectal fistulas of traumatic origin the authors distinguished the specific features of the clinical manifestations of the disease which must be taken into consideration in choosing the therapeutic tactics. In contrast to the management of common chronic paraproctitis, the treatment of traumatic rectal fistulas differs in principle, particularly when the internal opening of the fistula is in the wall of the rectal ampulla++. The authors determined the indications for various methods of treatment and techniques of operative interventions, including multistage surgical treatment with the creation of temporary colostomy.

Adolescent↗
PubMed1990

[Emoxipin pharmacokinetics in normal conditions and in models of experimental pathology].

The experimentally induced infarct and postoperative stress were shown to alter the kinetics of emoxipine consumption revealed in the increase of drug level in the blood. Elimination rate declines resulting in the increase of emoxipine bioavailability. This tendency is especially appreciable during elimination. The high emoxipine concentration appears to be the result of feedback regulation of its delivery from depot. Therefore pathological conditions have a significant effect on pharmacokinetics of emoxipine; this phenomenon seems to intensify the pharmacological action of this drug.

Animals↗
PubMed1989

Measurement of anomalously high hydration of (dA)n.(dT)n double helices in dilute solution.

Different DNA sequences have different physical properties, which seem to be important for their biological function. In particular, (dA)n.(dT)n has many unusual features, which include resistance to conformational changes in a variable chemical environment, an unusual thermodynamics of interaction with ligands, and the inability to reassociate into nucleosomes. Short A.T base-pair runs also play a critical role in DNA bending. It is believed that hydration of DNA is an important factor in determining the physical chemical and biological properties of different regions of DNA. Until now, however, it has not been possible to study the details of the hydration of DNA in dilute solution with sufficient sensitivity and precision. Moreover, it was not known if different base sequences differ in the extent of their hydration. Indirect evidence that (dA)n.(dT)n can be hydrated to a greater extent than other DNA sequences may be inferred from a recent study of the binding of drugs to polynucleotides. Here we used a novel high-precision technique measuring ultrasonic velocity to obtain direct estimates of the extent of hydration of various oligo- and polynucleotides in dilute solution. We report that different DNA sequences differ in their hydration, and that (dA)n.(dT)n in particular has an anomalously high level of hydration.

Base Sequence↗
PubMed1989

Site-specific laser modification (cleavage) of oligodeoxynucleotides.

Sequence-specific photomodification of oligodeoxynucleotide pAGAGTATTGACTTA ("a target") has been carried out with the aid of complementary fluorescent probes. Such a probe consisted of oligodeoxynucleotide pAATACTCT and a chromophore group attached to its 5' end. Three different derivatives of ethidium bromide were used as a chromophore. The photomodification was induced by nitrogen laser radiation (337 nm, 15 MW/cm2). The irradiation induces the following photodamages: target cleavage at the specific binding site with a cutting off of the 8-mer from its 5' end (yield up to 12%), formation of specific covalent adduct target-probe with a yield of 20-70%, and piperidine-sensitive target modifications with a 7-27% yield (for different chromophores). The total yield of specific photodamages of all kinds is 50-80%. The target cleavage and generation of piperidine-sensitive modifications are optically nonlinear processes. Piperidine treatment of the irradiated samples led to specific cleavage of the target with the yield up to 40%. All kinds of observed modifications are not influenced by high concentrations of free radical scavengers: 1.3M tBuOH and 10 mM cystamine. The pattern of cleavage indicates that the most probable position of the chromophore is between T8 and G9 of the target, i.e., the chromophore stacks on top of the last A.T base pair of the duplex. The aggregate of evidence is in agreement with the mechanism of nonlinear photomodification (the cleavage and generation of piperidine-sensitive modifications) based on the transfer of two-photon excitation energy from the chromophore to the target.

Base Sequence↗
PubMed1989

Free radical membrane scavengers in myocardium of rats of different age exposed to chronic hypoxia.

Age-dependent changes in myocardial content of vitamin E and total hydrophobic free radical scavengers were estimated in rats of different age. Comparatively high values of vitamin E (0.10-0.12 mg/g fresh tissue) were found in 2-day-old rats. The content of vitamin E was lower in 15- and 60-day-old and 40% higher in 120-day-old rats as compared with new-born animals. Total scavengers were monotonously falling down with age. Vitamin E contribution to total scavengers activity gradually increased in postnatal developmental period of cardiac muscle (from 10% for 2-day-old rats to 50% for 120-day-old rats). Chronic hypoxia (intermittent high altitude hypoxia - 7000 m) had no effect on the levels of cardiac total scavengers and vitamin E when the animals were acclimatized from the 5th postnatal day. Acclimatization of adult animals induced a drop in concentration of vitamin E and did not affect the level of total scavengers.

Aging↗
PubMed1989

[Complementary addressed modification of a hairpin-shaped model oligodeoxyribonucleotide].

A hairpin-shaped oligodeoxyribonucleotide d(pTTGGCACGAGCAGCCAA) (I) was alkylated with the reagent d(TTGGG) greater than UCHRCl (RCl = -C6H5-N(CH3)-CH2-CH2Cl) complementary to the hairpin's stem. Thermodynamic parameters for the hairpin structure estimated from melting curves were: delta Hh = -125 +/- 17 kJ/mol, delta Sh = -380 +/- 84 J/mol.K; and for the reagent - target complex delta Hpx = -155 +/- 8 kJ/mol, delta Spx = -427 +/- 21 J/mol.K. Effective constants of association Kx of the oligonucleotide with the reagent were determined at 30 and 50 degrees from the concentration dependence of the reaction yield and were 1988 +/- 83 and 1239 +/- 58 M-1, respectively. Experimental values of Kx agreed with the values of Kx = Kpx/(1 + Kh), calculated with the use of the thermodynamic parameters.

Autoradiography↗
PubMed1989

[A study of the conformational state of the ATP gamma-p-azidoanilide-Mn2+ complex by NMR and atom-atomic potential methods].

By means of H1 and P31 spin-lattice relaxation and atom-atomic potentials method it is shown that in aquous solution the ATP gamma-p-azidoanilide--Mn2+ complex occurs mainly as a mixture of two conformers in the ratio of 60:40. They both possess folded conformations with distances between aromatic rings 5-6 A, and adenine residue anti-oriented, the ribose and triphosphate chain conformations are 3E and gg, g'g', g'g', respectively, in the major conformer, and 2E and g'g', g'g', g'g' in the second conformer. Mn2+ ion forms 2-3 complexes with each conformer (the cation being differently coordinated) by substituting phosphoryl oxygens or N7 atoms of adenine for two water molecules in the hydration shell of the cation. Magnesium ion forms inner-sphere complexes with two out of four ion-coordination centres (P alpha, P beta, P gamma, N7(A] and outer-sphere complexes with two other centres.

Adenosine Triphosphate↗
PubMed1988

Complementary addressed modification of nucleic acids with the alkylating derivatives of oligothymidylate ethyl phosphotriesters. Effect of the phosphotriester fragments' configuration.

The alkylating derivatives of four individual diastereomers of the oligonucleotide [dTp(Et)]3dTpU and two individual diastereomers of oligonucleotide [dTp(Et)dTp]4 have been synthesized. The reagents with the phosphorus atoms in the enantiomeric p" configuration are shown to be more efficient in reacting with poly(dA) and with nucleic acids in Krebs-2 ascites carcinoma cells compared to those with the phosphorus atoms in the p' configuration.

Alkylation↗
PubMed1988

[Highly effective complementary addressed laser modification (cleavage) of oligodeoxynucleotides].

Complementary addressed nonlinear photomodification of oligodeoxynucleotide dAGAGTATTGACTTA ("target") has been carried out by means of fluorescent derivatives of oligonucleotide dpAATACTCT ("addressed chromophore"). Three different ethidium derivatives were used as a chromophore. The photomodification was induced by nitrogen laser radiation (337 nm, 15 MW/cm2), which led to the target cleavage in the addressation region with the yield of the main fragment (8 bases long) about 10%, formation of specific covalent adduct target-addressed chromophore with the yield 20-70%, "hidden" (not revealed by gel electrophoresis) target damages with 7-27% yield (for different chromophores). The total yield of specific (i. e. localized in the vicinity of the addressation site) modification was 50-80%. The target cleavage and hidden damage generation are optically nonlinear processes. Piperidine treatment of the irradiated samples caused addressed cleavage of the target with up to 40% yield. All kinds of observed modification are not effected by high concentrations of free radical scavengers, 1,3 M t-BuOH or 10 mM cystamine. The bulk of the data is in agreement with the mechanism of nonlinear photomodification (the cleavage and hidden damage generation) based on the transfer of two-photon excitation energy from the chromophore to the target.

Base Sequence↗
PubMed1988

[Mechanisms of the inhibition of Fe2+-induced oxidation of phosphatidylcholine by polyhydroxynaphthoquinones].

The kinetics of egg phosphatidylcholine oxidation induced by an artificial prooxidant Fe2+--ascorbate system or hematine was followed by oxygen uptake. The protective effect of natural free radical scavangers--polyhydroxynaphthoquinones, ionol (BHT), alpha-tocopherol and EDTA was estimated by the decrease of the phosphatidylcholine oxidation rate. EDTA was shown to inhibit the Fe2+--ascorbate-induced oxidation but had no effect on the hematine-induced oxidation. The inhibiting effect of polyhydroxynaphthoquinones on Fe2+--ascorbate-induced oxidation was 10-100 times as high as that on hematine-induced oxidation. The effects of BHT and alpha-tocopherol were the same in both models. Natural polyhydroxynaphthoquinones interacted with the free radical diphenylpicrylhydrazyl in stoichiometric ratios coinciding with the number of beta-hydroxyls in naphthoquinone molecules; the methylation of these hydroxyls fully suppressed such an interaction. Two possible mechanisms of action of polyhydroxynaphthoquinones as antioxidative agents are discussed. The first of these is coupled with the formation of Fe2+--PHNQ complexes, while the second one--with their effect as free radical scavengers. In both cases, beta-hydroxyls of naphthoquinone molecules were shown to play a key role.

Antioxidants↗
PubMed1987

[Prokaryotic and eukaryotic DNA-polymerase. I. The role of internucleotide phosphate groups in the binding of a primer with the enzyme].

The mechanism of binding and elongation of the oligothymidylate primers in the systems of the DNA polymerase alpha from human placenta and DNA polymerase I from E. coli with the poly(dA) as a template was investigated. Both dTMP and dTTP were shown to be the minimal primers of DNA polymerase alpha, the affinity and V increasing 1.8- and 1.4-fold respectively upon lengthening the primer by each unit from dTMP to d(Tp)9T. Further elongation is accompanied by 1.3-fold affinity enhancement and a decrease in V. For the E. coli enzyme, a similar dependence of affinity of primer d(Tp)4T-d(Tp)14T was observed with the inflexion point corresponding to d(Tp)8T. The individual diastereomers of oligothymidylate ethyl esters (with p' and p'' corresponding to enantiomeric configuration) such as d[Tp'(Et)Tp]3Tp'(Et)T, d[Tp''(Et)Tp]3Tp''(Et)T, d(Tp)8Tp'(Et)T, d(Tp)8Tp''(Et)T, d(Tp)8Tp'(Et)TpT, d(Tp)8 X X Tp''(Et)TpT and completely esterified analogues d[Tp(Et)]7T, d[Tp(Et)]14T were shown to initiate the poly (dA)-dependent polymerization catalyzed by both enzymes. A sum of the obtained results provided the basis for a number of conjectures on the mode of primer and template binding to the enzyme, possible role of their preformed complex, as well as electrostatic interactions and hydrogen bonding.

DNA Polymerase I↗
PubMed1986

Charge changes in sarcoplasmic reticulum and Ca2+-ATPase induced by calcium binding and release: a study using lipophilic ions.

Changes in the charge of sarcoplasmic reticulum (SR) vesicles are studied using lipophilic ions, which are adsorbed by the membrane phase. Upon addition of MgATP, phenyldicarbaundecaborane (PCB-) and tetraphenylboron (TPB-) are taken up by the SR vesicles, while tetraphenylphosphonium (TPP+) is released into the water phase. The PCB- uptake occurs as well under conditions when SR membrane is shunted by high Cl- concentration. MgATP induces minor additional binding of PCB- in the presence of oxalate and it is followed by release of the lipophilic anion from the vesicles. EGTA partly reverses the ATP effect, and calcium ionophore A23187 plus EGTA reverses it completely. Vesicles that were preliminarily loaded by Ca2+ demonstrated higher passive and lower ATP-dependent PCB- binding. Activation of isolated Ca2+-ATPase in the presence of 0.1 mM EGTA results in PCB- release into the medium and additional TPP+ binding to the enzyme. We suggest that the redistribution of the lipophilic ions between the water phase and SR membrane reflects charge changes in Ca2+-binding sites inside both SR vesicles and Ca2+-ATPase molecules in the course of Ca2+ translocation.

Adenosine Triphosphate↗