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A I Stepanov

Publications and source records attributed to A I Stepanov.

67 records · Page 4Linked to original sources
PubMedDate not supplied

Improvement of the model for calculation of relative sensitivity coefficients in inductively coupled plasma mass spectrometry.

Relative sensitivity coefficients (RSCs) were determined for 68 elements in inductively coupled plasma mass spectrometry (ICP-MS). It was shown that the Saha equation gives a rough description of ionization processes in ICP. A dependence of RSCs on the absolute electronegativity of atoms was found. This parameter is substantially affecting the accuracy of RSCs calculation for chemically active elements. Taking into account absolute electronegativities of the atoms for the calculation of RSCs, the ion formation processes in ICP-MS could be better described than by using first ionization potentials. The mean relative systematic error of RSCs calculation using absolute electronegativity was improved to 0.30.

Journal Article↗
PubMedDate not supplied

[Genetic bases for the selection of microorganisms using analogs].

The main mechanisms are considered for biosynthesis processes regulation by means of repression and inhibition with final products. On the basis of these mechanisms the state and prospects of the directed alteration of various stages in regulating the synthesis of primary and secondary metabolites, using breeding selection of mutants resistant to analogues are discussed. The main regularities are presented for using analogues of primary metabolites in the breeding strains with overproduction of various biologically active compounds.

Amino Acids↗
PubMedDate not supplied

[Extracellular alkaline ribonuclease of Bacillus thuringiensis var. subtoxicus].

Intraspecific selection of Bacillus thuringiensis strains producing extracellular alkaline ribonucleases was carried out. Subtoxicus subspecies with increased expression of the enzyme was detected. A method was developed to isolate preparative amounts of homogeneous extracellular RNase of B. thuringiensis var. subtoxicus. The physico-chemical and catalytic properties of the enzyme was studied and compared with extracellular RNases of others Bacillus species. The conclusion about the structural and evolutional conservation of Bacillus extracellular RNases was drawn.

Amino Acid Sequence↗
PubMedDate not supplied

[Regulation of amylolytic complex enzyme biosynthesis in Endomycopsis fibuligera strain 20-9].

The effect of glucose and cyclic 3',5'-adenosine monophosphate (cAMP) on the synthesis of glucoamylase and alpha-amylase by the yeast Endomycopsis fibuligera str. 20-9 was investigated. The glucoamylase synthesis was inhibited by every concentration (0.05--3.0%) of glucose. The synthesis of alpha-amylase was significantly reduced by high concentrations (2.0-3.0%) of carbohydrate only. An addition of cAMP (1 X 10(-5) M) reversed compeltely the inhibitory effect of 0.5-2.0% glucose on the alpha-amylase synthesis and partially restored the glucoamylase synthesis. It is concluded that catabolite repression may be involved in the regulation of alpha-amylase and glucoamylase synthesis by Endomycopsis fibuligera str. 20-9 and that this type of regulation shows varying effectiveness in the enzyme synthesis.

Amylases↗
PubMedDate not supplied

[Unusual structure of the regulatory region of the riboflavin biosynthesis operon in Bacillus subtilis].

In vitro mutagenesis with methylhydroxylamine and nitrosomethylurea was used to obtain a number of Bacillus subtilis mutants impaired in flavin-dependent response. Mutants displayed varying degree of flavin-dependent repression of riboflavin synthase and of 6,7-dimethyl-8-ribityl-lumasine accumulation. Single nucleotide substitutions were detected by DNA sequencing in all of the mutants, affecting the 48 b.p. target area between the mRNA start and the AUG of the first gene.

Bacillus subtilis↗
PubMedDate not supplied

[Cloning of genetic material in Bacillus].

Plasmid vectors capable for propagation of Bacillus subtilis DNA fragments containing riboflavin genes were constructed. Cloning of rib operon using pUB110 derivatives was performed in recE4 strain by using sequentional rescue of plasmids containing subfragments of the operon. Also, rib operon was cloned on the vectors containing DNA repeats. It was shown that the presence of direct and inverted repeats within plasmids allows to transform B. subtilis cells by monomers of plasmid DNA. Vectors that contained repeated sequences of DNA and ensured efficient cloning of genetic material in B. subtilis recipient cells were constructed. The use of streptococcal plasmid pSM19035 allowed to obtain vectors which were suitable for cloning large DNA fragments (6 MD and even more) in B. subtilis. A model of B. subtilis transformation by various types of plasmid DNA is presented. The model is in agreement with the general conception of chromosomal DNA transformation.

Bacillus subtilis↗