Biochemical and Biophysical Research Communications
Regular ArticleBenzo(a)Pyrene Hydroxylase Activity in Yeast Is Mediated by P450 Other Than Sterol 14α-Demethylase
Abstract
Benzo(a)pyrene hydroxylation has been observed in Saccharomyces cerevisiae and the role of sterol 14α-demethylase (CYP51A1) in this activity has been examined by using a strain which contains a gene disruption of CYP51A1. This strain still contained P450 protein(s) with a Soret absorption maximum at 448nm in reduced carbon monoxide difference spectra of the microsomal fraction. On addition of benzo(a)pyrene to this microsomal extract a typical Type I substrate-binding spectrum was obtained and was also observed for the isogenic sister strain containing no CYP51A1 gene disruption. Microsomal extracts of both strains had equivalent activity in the aryl hydrocarbon hydroxylase assay. These results indicate a yeast benzo(a)pyrene hydroxylase activity distinct from sterol 14α-demethylase P450.
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Effect of Salmonella assay negative and positive carcinogens on intrachromosomal recombination in S-phase arrested yeast cells
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Chloroform and carbon tetrachloride induce intrachromosomal recombination and oxidative free radicals in Saccharomyces cerevisiae
1998, Mutation Research - Fundamental and Molecular Mechanisms of MutagenesisChlorination of drinking water results in the generation of low levels of numerous chlorinated hydrocarbons due to the reaction of chlorine with naturally occurring organic compounds in the water. Concern has been raised about the safety of these chlorinated contaminants as several of them, most notably chloroform (trichloromethane), have been shown to be carcinogenic in long-term rodent bioassays and weak correlations between trihalomethane levels in drinking water and an increased risk of bladder and colorectal cancer in humans have been found. Chloroform and carbon tetrachloride induce liver cancer in rats and mice only at doses where significant hepatotoxicity is observed and have been classed as non-genotoxic carcinogens. We have investigated the ability of chloroform, carbon tetrachloride and 1,1,1-trichloroethane to induce deletions via intrachromosomal recombination in the yeast Saccharomyces cerevisiae. Chloroform and carbon tetrachloride induced this genotoxic recombination event at similar doses, 1,1,1-Trichloroethane gave only a weak response in the DEL recombination assay and only at the highest dose. We further show that chloroform and carbon tetrachloride, but not trichloroethane, induced oxidative free radical species in our yeast strain. The free radical scavenger N-acetylcysteine reduced chloroform-induced toxicity and recombination, and both chloroform and carbon tetrachloride were able to oxidize the free radical-sensitive reporter compound dichlorofluorescein diacetate in vivo. The implications of these findings to the carcinogenic activities of the three compounds are discussed.
Diaminotoluenes induce intrachromosomal recombination and free radicals in Saccharomyces cerevisia
1997, Mutation Research - Fundamental and Molecular Mechanisms of MutagenesisThe carcinogenicity of aniline-based aromatic amines is poorly reflected by their activity in short-term mutagenicity assays such as the Salmonella typhimurium reverse mutation (Ames) assay. More information about the mechanism of action of such carcinogens is needed. Here we report the effects on DEL recombination in Saccharomyces cerevisiae of the carcinogen 2,4-diaminotoluene and its structural isomer 2,6-diaminotoluene, which is reported to be non-carcinogenic. Both compounds are detected as equally mutagenic in the Salmonella assay. In the absence of any external metabolizing system both compounds were recombinagenic in the DEL assay, with the carcinogen being a more potent inducer of deletions than the non-carcinogen. In the presence of Aroclor-induced rat liver S9, however, the carcinogen 2,4-diaminotoluene became a 2-fold more potent inducer of deletions, and the non-carcinogen 2,6-diaminotoluene was rendered less toxic and no induced recombination was observed. 2,4-Diaminotoluene is distinguished from its non-carcinogen analog in the DEL assay, therefore, on the basis of a preferential activation of the carcinogen in the presence of a rat liver microsomal metabolizing system. Free radical species are produced by several carcinogens and have been implicated in carcinogenesis. We further investigated whether exposure of yeast to either 2,4-diaminotoluene or 2,6-diaminotoluene resulted in a rise in intracellular free radical species. The effects of the free radical scavenger N-acetylcysteine on toxicity and recombination induced by the two compounds and intracellular oxidation of the free radical-sensitive reporter compound dichlorofluorescin diacetate were studied. Both 2,4- and 2,6-diaminotoluene produced free radical species in yeast, indicating that the reason for the differential activity of the compounds for induced deletions is not reflected in any difference in the production of free radical species.