PubMed Health⌕ Search

Biomedical subjects

A A Akhrem

Publications and source records attributed to A A Akhrem.

162 records · Page 9Linked to original sources
PubMedDate not supplied

[Effect of phospholipids on the activity of highly-purified liver microsome cytochrome P-450 in a reaction of aniline and naphthalene hydroxylation by hydroperoxides].

The effect of different phospholipids on the functional activity of highly purified cytochrome P-450 used as a co-substrate of cumene hydroperoxide was examined. At the molar ratio of phospholipids to cytochrome P-450 that was equal to 30, phosphatidyl serine, phosphatidyl inositol, the total fraction of microsomal phospholipids, and lysophosphatidyl choline increased the hydroxylation rate of aniline and naphthalene. The effect of the above phospholipids on the rate of naphthalene oxidation was much more pronounced. Phosphatidyl choline and sphingomyelin in similar large quantities did not exert a stimulating effect on the reactions studied. The kinetic parameters of aniline oxidation in the systems containing phospholipids that produced an activating effect were investigated.

Aniline Compounds↗
PubMedDate not supplied

[Nucleoprotein fusion. III. Causes and conditions for development of the multiphase character of the DNA--protein fusion curve].

The influence of proteins reversibly and irreversibly bound to DNA on the shape of melting curve has been considered. It is shown that the melting curve becomes biphasic in two cases: (i) cooperative binding of proteins with DNA (II) STRONG DIFFERENCE IN THE BINDING CONSTANTS WITH HELICAL AND COILED REGIONS. Simple formulae permitting to determine which of two causes stipulate for biphasic profile of a given experimental melting curve are obtained. Melting curves of DNA-basic oligopeptides complexes have been investigated. It is shown that the oligopeptides, when their chain length does not exceed 10, are able to migrate along DNA and biphasic shape of the melting curve is stipulated by the cooperative manner of their binding with DNA.

DNA↗
PubMedDate not supplied

[Effect of the size of the ligand molecule on the stability of the DNA double helix].

The influence of ligand length on helix-coil transition parameters in the presence of different ligand concentrations has been considered theoretically. A decrease of this influence with an increase of ligand length when the binding constant has a constant value was shown. When binding free energy is proportional to the ligand length, i. e. when K = K0m (K-binding constant, m-ligand length) the length effect is unambigous. In the presence of low-ligand concentration the stability of DNA double helix increases with their length, whereas in the presence of high concentrations it decreases.

DNA↗
PubMedDate not supplied

[Theoretical conformational analysis of delta-sleep inducing peptide].

The spatial structure of o-sleep-inducing peptide has been determined by means of semi-empirical conformational analysis of its overlapping fragments. Possible intramolecular contacts in the most stable conformations are discussed. The essential role of electrostatic interactions is emphasized.

Delta Sleep-Inducing Peptide↗
PubMedDate not supplied

[Effect of selectively reacting ligands on the helix-coil transition of DNA. III. Calculation of the melting curves of DNA-ligand complexes].

The calculation of variations in the helix-coil transition parameters, melting curves and differential melting curves of DNA characteristic of different degree of heterogeneity in the presence of ligands interacting selectively with a certain type or types of base pairs has been carried out. It has been shown that ligands with a selective and non-selective manner of binding influence identically the denaturation process in the case of low DNA heterogeneity (synthetic periodic polynucleotides and satellite DNA fractions). In the case of high heterogeneity (the main fraction of DNA of higher organisms) this influence is quite different. The phenomenon of AT- and GC-base pairs thermostability inversion is considered.

Animals↗
PubMedDate not supplied

[Effect of selectively reacting ligands on the helix-coil transition of DNA. IV. Heat denaturation of DNA in an acid medium].

The DNA thermal denaturation in acidic medium has been investigated experimentally and theoretically. The formulae describing a dependence of the helix--coil transition parameters (melting temperature (Tm) and melting range width (delta T) on ionisation constants values of all kinds of DNA bases in the helix and coil regions and medium acidity have been obtained. Dependences Tm (pH) and delta T (pH) have been determined experimentally and calculated for different models of protonation. Based on the comparison of theoretical and experimental dependences Tm (pH) and delta T (pH) a strict examination of the theory is conducted. The mechanism of DNA protonation is discussed.

Animals↗
PubMedDate not supplied

[Heat inactivation of cytochrome P-450].

Thermal inactivation of cytochrome P-450 in different states (microsomes, highly purified and immobilized), characterized by the loss of catalytic activity in cumene hydroperoxide--dependent aniline hydroxylation has been studied in the temperature range 40-58 degrees C. The process of thermoinactivation is characterized by the first order rate constants. From the temperature dependence of these constants the energy of activation and the activation parameters of cytochrome P-450 thermoinactivation have been determined at 45 degrees C. In the presence of 20% glycerol the activation parameters of cytochrome P-450 thermoinactivation in microsomes in highly purified and immobilized states are very similar.

Animals↗
PubMedDate not supplied

[Multiphasic character of the kinetics of cytochrome P-450 destruction in microsomal LM2- and LM4-forms in the reaction with cumene hydroperoxide].

Cytochrome P-450 destruction kinetics by cumene hydroperoxide has been studied in LM2 and LM4 microsomal and purified forms. Three destruction phases of cytochrome P-450 were shown to be observed irrespective of the source and integration degree, cytochrome P-450 pseudomonomolecular consumption rate constants being dependent in a complex way upon the cumene hydroperoxide initial concentration. The radical character of cytochrome P-450 destruction was proved by experiments with 1-naphtol. The mechanism of radicals formation is discussed.

Animals↗
PubMedDate not supplied

[Immobilization of cytochrome P-450 from rabbit liver microsomes on albumin modified Sepharose 2B].

A highly purified cytochrome P-450 from rabbit liver microsomes has been immobilized on albumin modified omega-aminohexyl-Sepharose 2B, after glutaraldehyde treatment of the matrix. The effect of the degree of albumin modification of the matrix on the catalytic activity of immobolized cytochrome P-450 has been studied in cumene hydroperoxide dependent aniline hydroxylation. On this basis an optimal cytochrome P-450/albumin ratio has been found which allows a substantial decrease in the rate of cytochrome P-450 destruction by cumene hydroperoxide in the substrate absence.

Albumins↗
PubMedDate not supplied

[Effect of changes in the stoichiometry of DNA--ligand complexes during heat denaturation of DNA on helix-coil transition parameters].

The influence of a change in DNA-ligand complex stoichiometry in the process of denaturation on temperature and temperature range width of helix-coil transition (Tm, delta T) has been considered. The stoichiometry is characterized by two parameters: by the number of base pairs covered with one ligand (m) and by the number of base pairs per one binding centre (r). It is shown that the change of r and m during denaturation strongly influences the DNA melting process. If the product rm doesn't change during denaturation, the melting temperature shift caused by a ligand concentration growth has a finite limit. If r1m1 not equal to r2m2 (index 1 is related to the coil DNA from and index 2--to the helix DNA form), the melting temperature during concentration growth aspires to + infinity, when r1m1 > r2m2, and to absolute zero, when r1m1 < r2m2. The sign of the effect (stabilization or destabilization) is independent of a binding constant and a factor of cooperativity of DNA-ligand interaction. Dependences of Tm and delta T on ligand concentration for different r1, r2, m1, m2 are analysed.

Chemical Phenomena↗
PubMedDate not supplied

[Nucleoprotein melting. II. Melting of irreversible DNA-protein complexes].

Three with different complexity models: single-stranded, periodic theeropolymer, two-stranded periodic heteropolymer and complex of DNA with irreversible bound proteins have been considered. It is shown that the individual bands on the differential melting curve appear if the length of protein bound regions exceed 25 base pairs. In this case the melting temperature of free and protein bound regions depends on their reciprocal length in almost linear manner. Moreover, the temperature of the peak corresponding to the protein bound regions is independent on the length of the adjacent free DNA regions if their length exceeds 15 base pairs. If the length of free and protein bound regions exceed 300 base pairs, their melting temperatures becomes almost equal to that of infinitely long polymer with the analogous structure. A simple method for determination of length of the free and the protein bound regions length has been proposed.

DNA↗
PubMedDate not supplied

[Model of the spatial structure of peptide T].

The spatial structure model of peptide T (AIDS reproduction inhibitor, the amino acid sequence of which corresponds to the fragment into the binding site of the virus protein gp120 with T4 receptor) is proposed. Peptide structure modelling has been carried out by the previously developed method based on joint usage of the molecular mechanics algorithms and NMR spectroscopy data. To build the model, two-dimensional nuclear Overhauser effect spectroscopy data for RNase A homologous fragment 22-26 were taken from the literature. The result of the presented work was a set consisting of six types of low-energy structures with different spatial packing of the peptide main chain. All structural types have been shown to be characterized by the lack of strict determination of the side chain conformations of the amino acid residues that can be realized in a few states providing approximately equal (within the given type) stabilization of one main chain form. At the same time, despite the definite differences, all of the selected structures were characterized by the presence of two consecutive reverse polypeptide chain turns at the C-terminal pentapeptide fragment. This site is supposed to be responsible for the peptide binding with T4 receptor and the antiviral effect.

Algorithms↗
PubMedDate not supplied

[The resistance of liposomes as potential drug carriers to the action of phospholipase A2].

Stability of liposomes with varied phospholipid (PL) content towards the action of phospholipase A2 (PLA2) was studied in vitro. Liposomes were prepared of phosphatidylcholine (PC), phosphatidylglycerol (PG), phosphatidylethanolamine (PE), and phosphatidylinositol (PI) and their mixtures with sphingomyelin (SM). PC and PG liposomes were also treated with PLA2 in the presence of a number of proteins such as cytochrome c, cytochrome b5, cytochrome P-450, polylysine, and histone H1. Among all the liposomes studied PG-containing ones were found to be most stable towards PLA2. In SM-containing liposomes, the levels of PG, PI, PE and PC after 20 min of hydrolysis were 65, 62, 55 and 50%, respectively. In PC + PG liposomes, the PC content after treatment with PLA2 was by about 15-20% higher than in control PC liposomes. The addition of all the proteins studied influenced significantly stability of both PC and PG in two-component PL liposomes, but had no effect on liposomes consisting only of PC. The incorporation of the integral membrane protein cytochrome P-450 into PC and PG liposomes caused a decrease in their stability towards PLA2, the decrease depending on the lipid/protein molar ratio.

Drug Carriers↗