PubMed Health⌕ Search

Biomedical subjects

S M Navashin

Publications and source records attributed to S M Navashin.

At least 109 records · Page 6Linked to original sources
PubMed1983

[Free radical mechanism of action of pyrimido-triazine antibiotics].

EPR spectra of anion radicals were recorded as a result of chemical or enzymatic reduction at various pH of the pyrimido-triazine antibiotics. These anion radicals easily form superoxide radicals in the presence of oxygen. It is supposed that a higher selectivity of reumycin action is due to difference in the redox potentials of the neutral and ionized antibiotic forms. A possibility of enhance the reumycin potency may involve the pH lowering inside the tumor cells - for example, by glucose injections.

Animals↗
PubMed1983

[Can extrachromosomal genetic elements be recognized as inventions?].

The legal bases for acknowledgement of plasmids (vectors) as inventions, in particular within the classes of the "substance" and "microbial strain" are discussed. There is a definite similarity in a number of features between phages recognized as inventions and plasmids. Therefore, in principle their acknowledgement as inventions may be considered possible, since it raises no new problems as those occurring in legal protection of microbial strains. At the same time there is no pressing need in acknowledgement of plasmids (vectors) as inventions and their legal protection should be rather of the prestige character.

Extrachromosomal Inheritance↗
PubMed1983

[Pharmacokinetic basis for using tobramycin and sisomicin in treating pyelonephritis of the transplanted kidney].

The pharmacokinetics of tobramycin and sisomicin in patients after kidney transplantations was studied. A significant variability of the pharmacokinetic parameters of tobramycin and sisomicin under conditions of the changing function of the kidney transplant was shown. This required individual control of the drug serum levels in such patients. Linear correlation between the exponent (beta) and the clearance of endogenous creatinine was observed. On the basis of this correlation a nomogram providing a decrease in the percentage of the errors in determining the dosage intervals was plotted.

Adolescent↗
PubMed1983

[TEM-type beta-lactamase coded by the plasmid from Citrobacter sp].

beta-Lactamase was isolated from the cells of E. coli, strain 1039, a transconjugant carrying the plasmid first detected in Citrobacter sp. beta-Lactamase was purified to obtain a homogeneous preparation. The activity of the enzyme was estimated by a modification of the potentiometric method providing determination of up to 0.1 mumol of penicilloinic acid. The activity of the pure enzyme was 206 mumol per 1 mg of protein per minute. The molecular weight determined by gel filtration was 21500. The substrate profile of beta-lactamase corresponded to the TEM type. Preliminary incubation with methicillin resulted in a significant decrease in the enzyme activity. Carbenicillin, dicloxacillin, oxacillin and cephalothin induced no decrease in the activity of the enzyme when subjected to preliminary incubation with it. The use of the functional group reagents allowed detecting residues of serine and lysine in the enzyme active centre or close to it. Km and Kcat for some antibiotics were evaluated. The ratio of alpha- and beta-structures in the molecule of beta-lactamase was determined with the method of circular dichroism (CD). The fraction of the alpha-spiral areas amounted to 30 +/- 5 per cent and the fraction of beta-structures amounted to 20 +/- 5 per cent. On attachment of methicillin to the molecule of the enzyme the ratio of alpha- and beta-structures did not change which may be considered as a preliminary indication of the centre "immobility" in the process of catalysis. Slow hydroysis of methicillin by beta-lactamase was shown with the method of CD.

Chemical Phenomena↗
PubMed1982

[Genetic control of antibiotic resistance and the R plasmid properties of clinical E. coli strains].

The electrophoretic analysis of the plasmid DNA of multiresistant clinical E. coli strains revealed the presence of extrachromosomal DNA in 97% of the strains. The plasmid nature of resistance was established in 88-100% of E. coli strains resistant to chloramphenicol, ampicillin, streptomycin or kanamycin and in 67% of the strains resistant to tetracyclin. 24 out of 40 strains contained conjugative R-plasmids in which the determinants of resistance to kanamycin, ampicillin and chloramphenicol were transferred most frequently (82-93%), while the determinants of resistance to tetracyclin and streptomycin were transferred less frequently (45% and 35%, respectively). Nonconjugative R-plasmids were detected in 15 out of 40 antibiotic-resistant strains; in these plasmids the determinants of resistance to streptomycin (65%) and tetracyclin (22%) were transferred most frequently.

Anti-Bacterial Agents↗
PubMed1982

[Methodological approaches to controlling the antibiotic content in disks for determining microorganism antibiotic sensitivity].

The content of antibiotics in the discs is the main requirement to their quality. There are 2 methods for determination of the antibiotic content in the discs: (1) a method with preliminary extraction of the antibiotic from the disc followed by determination of its content in the extract biologically and (2) a method using 3 or more standard discs containing different amounts of the antibiotic. A study was performed to show the advantages and limitations of the methods. The conditions for determination of the activity of 22 antibiotics contained in the discs with the method using the standard discs were developed. Comparison of the results obtained with the 2 methods showed that they did not differ significantly. However, it is considered advisable to use for the disc control the method based on direct diffusion of the antibiotic from the disc into agar, since in this case the antibiotic amount in the disc is determined under conditions as much as possible close to the conditions of the disc using for determination of the microbial antibiotic sensitivity.

Anti-Bacterial Agents↗
PubMed1981

[Changes in microorganism sensitivity to antibiotics as affected by divalent metal ions].

Ca+ and Mg+ in nutrient media significantly influence the results of antibiotic sensitivity determination in microorganisms. The data of the study are indicative of a necessity for the media standardization with respect to the content of bivalent metal ions. It is recommended that agar-agar manufactured by the South Sea Factory (tafuinsky) be used for preparation of nutrient media for determination of microbial sensitivity to antibiotics and Hottinger meat pancreatic digest as the nitrogen source providing the content of 120 mg per cent of amine nitrogen in the medium.

Anti-Bacterial Agents↗
PubMed1981

[Role of plasmid genes in neomycin synthesis].

Comparative investigation of the neomycin-producing strain and a strain which has spontaneously lost the capacity for the antibiotic synthesis suggested participation of the plasmid with the molecular weight of 59 X 10(6) dalton in determination of the biosynthesis of neomycin and phosphotransferase inactivating the antibiotics. This plasmid factor is not eliminated under the effect of the sublethal concentrations of acridine orange and ethidium bromide.

Acridine Orange↗
PubMed1980

[Properties of aminoglycoside-3'-phosphotransferases determined by kanamycin transposones Tn 601 and Tn 5].

Aminoglycoside-3'-phosphotransferase I and II (APT-3'-I and APT-3'-II) has been purified to homogenity from the cells of E. coli containing the plasmids R6 and JR67, respectively. The purification procedure involved competitive affinity chromatography on neomycin-sepharose and gel-filtration on Sephadex G-100. The specific activity of APT-3'-I with the substrates--lividomycin A, neomycin B, paromycin, ribostamycin, kanamycins A and B--are 4.3, 2.8, 2.1, 1.6, 0.9 and 0.8 mol/min. mg protein, respectively. The specific activity of APT-3'-II with the substrates--ribostamycin, paromycin, kanamycins A and B, neomycin B--are 8.0, 7.2, 4.0, 4.5 and 3.6, respectively. Mg2+ is required for the activity of both enzymes. Co2+, Zn2+ and Mn2+ are active in case of APT-3'-I; however, these cations are less active than Mg2+. The pH-optimum of APT-3'-I and APT-3'-II is 7.0--7.5. High ionic strength is required for the activity of both enzymes. The molecular weights of APT-3'-I and APT-3'-II are about 36 000 and 26 000, respectively. The amino acid composition of APT-3'-I and APT-3'-II was determined. Both enzymes contain tryptophane residues whose fluorescence intensity decreased when ATP, but not amino-glycoside antibiotics, is added. The interrelationship between the molecular weights of these enzymes and the sizes of the loops of transposones Tn 601 and Tn 5, encoding APT-3'-I and APT-3'-II, is discussed.

Amino Acids↗