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Biomedical subjects

A S Khokhlov

Publications and source records attributed to A S Khokhlov.

At least 19 recordsLinked to original sources
PubMed1988

[Hybridization of A-factor deficient mutants of Streptomyces griseus by means of fusion of protoplasts].

Characteristics of 6 A-factor deficient mutants of S. griseus are presented. The common feature of the mutants was impairment of sporulation, formation of aerial mycelium and streptomycin synthesis. Pair-by-pair hybridization of the mutants was performed with protoplast fusion followed by regeneration. 9 pair couplings of the mutants were performed. In 3 of them sporulating recombinants were detected. The antibiotic production level in 70 hybrids was different and ranged from 0 to 1700 micrograms/ml. The morphological features of the colonies and the number of the spores formed were also different. The common feature of all the 70 sporulating hybrid strains was recovery of synthesis of A-factor, an endogenic regulator of S. griseus development. Therefore, in the A-factor deficient mutants impairment of A-factor synthesis was induced not by the plasmid elimination, as was suggested, but by mutation of separate genes.

4-Butyrolactone↗
PubMed1979

Myo-inositol-1-phosphate synthase from streptomyces griseus (studies on the biosynthesis of cyclitols, XXXVIII).

It could be shown that Streptomyces griseus, the microorganism producing the antibiotic streptomycin and also mutant strains of this species that cannot synthesize streptomycin, possess myo-inositol-1-phosphate synthase (EC 5.5.1.4), the enzyme cyclizing D-glucose 6-phosphate. The enzyme isolated from that organism is extremely instable, its molecular weight is approximately 260,000, and it requires a divalent metal ion for its activity. This is the first instance that an enzyme of this specificity has been found in a prokaryotic organism.

Carbohydrate Epimerases↗
PubMed1979

Influence of A-factor on the ultrastructure of the A-factor deficient mutant of Streptomyces griseus.

The fine structure of the A-factor deficient mutant strain of Streptomyces griseus grown in the absence or in the presence of this factor was studied by transmission electron microscopy. The submerged 96 h culture grown in the presence of the A-factor was characterized by the formation of a large amount of spores accompanied by mycelium disintegration. A number of essential ultrastructural changes were observed in the mycelium in the course of development and streptomycin biosynthesis after the A-factor addition. Thus, the cell wall was transformed in another manner at various developmental stages. For a long time the associated ribosomes were preserved. The number of intracytoplasmic membrane structures increased. New, unusual organelles appeared which consisted of parallel cylindrical structures. The possible nature of these organelles is discussed.

4-Butyrolactone↗
PubMed1978

[Slightly active Actinomyces streptomycini (Streptomyces griseus) mutants having a protein in the biosynthesis of the streptidine portion of the streptomycin molecule].

Twelve mutants having a block in biosynthesis of the streptidine part of the streptomyciu molecule were selected under the effect of nitrozomethylbiuret. These 12 strains responded by an increase in the level of the antibiotic production to the addition of streptidine to the cultivation medium. The complementation analysis showed that every streptidine-dependent mutant interacted at least with 2 other mutants. On the basis of the data obtained it is possible to conclude that all 12 mutants had blocks in streptidine biosynthesis but at different stages of this complicated process.

Bacterial Proteins↗
PubMed1978

[Interaction of streptidin-dependent Actinomyces streptomycini (Streptomyces griseus) mutants No. 170 and 145 with mutants having blocks at various stages of streptomycin biosynthesis].

In complementation analysis of low active streptidine dependent strains of Act. streptomycini, 170 and 145 with mutants having different blocks in biosynthesis of streptomycin it was found that these strains were the donors of some thermostable substances and could reduce the biosynthesis of streptomycin in the mutants having impairements in biosynthesis of streptidine and streptobiosamine, as well as in a number of strains with unknown blocks. It is supposed that the substances produced by mutants 170 and 145 were intermediate products in streptomycin biosynthesis.

Cyclohexanols↗
PubMed1978

[Actinomyces streptomycini mutants blocked in the biosynthesis of the streptobiosamine portion of the streptomycin molecule].

Four low active mutants of Act. streptomycini were obtained under the effect of nitrozo-methylbiuret. The mutants increased their antibiotic production level, when streptobiosamine was present in the formentation medium. It was shown that in 3 out of the 4 mutants the highest antibiotic yield was in the medium containing streptobiosamine in an amount of 1 mg/ml and in 1 strain the highest yield was in the medium with 0.5 mg/ml of streptobiosamine. When the mutants were grown in a medium containing N-methyl-L-glucosamine no increase in streptomycin production was registered.

Biuret↗
PubMed1977

[Induced variability of Streptomyces galbus].

A-factor, a regulating substance is an obligatory participant of streptomycin biosynthesis by Str. griseus. Str. galbus also synthesizes streptomycin but without participation of A-factor. Mutant with various morphological properties were obtained under the effect of ethylenimine. No correlation between spore formation and streptomycin synthesis was found in the mutants of Str. galbus unlike Str. griseus. Correlation between a decrease in the capacity for production of a dark brown pigment and an increase in the level of streptomycin biosynthesis was shown: the mutants with the dark brown pigment did not synthesize streptomycin, while the mutants without the pigment synthesized streptomycin in the amounts 10-14 times higher than those in the initial strain. The same as the initial strain, the mutants of Str. galbus had no A-factor and did not respond to its addition into the medium by changing their properties and streptomycin synthesis.

Aziridines↗
PubMed1976

Chemical studies on actinoxanthin.

The antitumor protein actinoxanthin exhibits high inhibitory activity against a number of gram-positive bacteria and some strains of transplantable leucoses and related tumors. Actinoxanthin was shown to consist of a single polypeptide chain crosslinked by two disulfide bonds and to contain 107 amino acid residues. Reduced and alkylated actinoxanthin was digested with chymotrypsin, thermolysin and trypsin. Based on the sequence analysis of fragments so obtained the complete amino acid sequence and the location of disulfide bonds of actinoxanthin has been proposed. The high degree homology of some regions of actinoxanthin and the antitumor protein neocarzinostatin have been revealed.

Alkylation↗
PubMed1975

[Characteristics of the interaction of the A-factor with mutant 1439 of Act. streptomycini in the biosynthesis of streptomycin].

Some peculiar properties of A-factor using by mutant 1439 of Act. streptomycini were studied. It was found that A-factor was most intensively used for biosynthesis of streptomycin when it was added during inoculation. When A-factor was added to a I- or 2-day culture it was required in 10 times higher amounts and its high non-specific adsorption by the mycelium was observed. Interaction of A-factor with the mycelium providing restoration of the biosynthetic process was very rapid on a short-term contat of the I-day culture with A-factor. Transformations occurring under the effect of A-factor and leading to formation of streptomycin took place mainly inside the cells. Changes in the life cycle induced by A-factor developed under different conditions as compared to those promoting streptomycin biosynthesis.

Bacteriological Techniques↗