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K Alexandrov

Publications and source records attributed to K Alexandrov.

At least 73 records · Page 4Linked to original sources
PubMed1979

[Demonstration of "hydroxylase" and "epoxide hydrase" activities in preparations of nucleoli isolated from rat liver].

Aryl hydrocarbon hydroxylase (AHH) activity and epoxyde hydrase (EH) activity have been found in Rat liver nucleoli obtained from untreated (C) and methylcholanthrene (MC) pretreated Rats. Electron microscopic observations of nucleolar preparations did not reveal significant contamination either by intact nuclei or by nuclear membranes. Very low but detectable activity of NADPH cytochrome C reductase was found in the nucleoli. Nucleolar preparations revealed little AHH activity (12-18 pmoles/min/mg). AHH was inducible by MC in nuclei but not in nucleoli. The presence of EH in nucleoli was demonstrated with phenanthrene 9,10-oxide (550-620 pmoles/min/mg) and benzopyrene 4,5-oxide (92-116 pmoles/min/mg). These values were lower than those obtained using intact nuclei. The addition of TCPO (10(-4) M) inhibited EH activity.

Animals↗
PubMed1977

Influence of inducers and inhibitors of mixed-function oxidasts on benzo(a)pyrene binding to the DNA of rat liver nuclei.

Benzo(a)pyrene-conjugated DNA was isolated after benzo(a)pyrene was incubated in vitro with liver nuclei from control, phenobarbital-treated, and methylcholanthrene-treated rats and the reduced nicotinamide adenine dinucleotide phosphate-generating system. Aryl hydrocarbon hydroxylase, the levels of activity of which varied with the different nuclear systems, was highly specific in the activation of the benzo(a)pyrene to forms that bind to DNA. Sephadex LH-20 chromatography of the degreded DNA from liver nuclei of pretreated rats revealed an in vivo DNA-bound product previously shown to be derived from 7,8-dihydro-7,8-dihydroxybenzo(a)pyrene 9,10-oxide (Product A). The nuclei from phenobarbital-pretreated rats also contained a DNA-bound product corresponding to that derived from the binding of benzo(a)pyrene 4,5-oxide (Product C), but they completely lacked the DNA-bound product derived from futher metabolism of 0-hydroxybenzo(a)pyrene (Product D). In contrast, nuclei from methylcholanthrene-treated rats yielded large amounts of Product D. No bound products were found with the control nuclei. 7,8-Benzoflavone caused an 80% inhibition of benzo(a)pyrene binding to DNA in the nuclei of methylcholanthrene-pretreated rats, but it had no effect on control nuclei or those from phenobarbital-pretreated rats. It inhibited formation of Product A, but not Products B or C, in nuclei from phenobarbital-pretreated rats. With nuclei from methylcholanthrene-pretreated rats. With nuclei from methylcholanthrene-pretreated animals, 7,8-benzoflavone led to an overall loss of products, but small amounts of Products A and B persisted. 1,1,1-Trichloropropene 2,3-oxide strongly inhibited nuclear aryl hydrocarbon hydroxylase activity and the phenol fraction measured by thin-layer chromatography in all nuclear systems, but it significantly increased the benzo(a)pyrene binding in all nuclei. With nuclei from phenobarbital-treated rats, it inhibited the formation of Product B but not of Products A and C; whereas with nuclei from methylcholanthrene-pretreated rats, it inhibited the fromation of all the hydrocarbon-deoxyribonucleoside products.

Animals↗
PubMed1976

Comparison of the metabolism of benzo[alpha]pyrene and binding to DNA caused by rat liver nuclei and microsomes.

Administration of 3-methylcholanthrene (3MC) to rats greatly enhanced the aryl hydrocarbon hydroxylase (AHH) activity of liver nuclei. However, the binding in vitro [3H]benzo[alpha]pyrene (BP) to DNA within the nuclei which occurred at the same time as hydroxylation of BP was much less enhanced. Thin layer chromatography of the metabolites of BP produced by these nuclei revealed the same metabolites in similar relative amounts as were produced by rat liver microsomes prepared from rats which had received 3MC. The binding to DNA was further analysed by hydrolysis of the DNA and fractionation on a Sephadex column. This analysis revealed that the binding to DAN in nuclei was very similar in nature to that which occurred when calf-thymus DNA was added to microsomes metabolising BP.

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PubMedDate not supplied

Diversity and phylogeny of insect trypanosomatids based on small subunit rRNA genes: polyphyly of Leptomonas and Blastocrithidia.

With the aim of further investigating phylogenetic relationships in insect trypanosomatids, we have determined the sequences of small subunit rRNA genes from ten isolates, which were originally classified as Leptomonas, Blastocrithidia, and Wallaceina based on their morphology in the hosts. The inferred maximum likelihood, parsimony, and distance trees indicate that the Leptomonas and Blastocrithidia are polyphyletic, and confirm the polyphyly of Herpetomonas and Crithidia. Blastocrithidia triatoma and Leptomonas collosoma were among the earliest branching lineages among the insect trypanosomatids, while most other isolates were found within a closely related terminal clade, which also included Crithidia fasciculata. This analysis has clearly demonstrated that the morphological classification system of insect trypanosomatids does not always reflect their genetic affinities warranting its revision in the future.

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