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Results for “BENZOPYRENES”

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PubMed1979

Modulation of the in vivo covalent binding of the carcinogen benzo(a)pyrene to rat liver DNA by selective induction of microsomal and nuclear aryl hydrocarbon hydroxylase activity.

The influence of microsomal (mAHH) and nuclear (nAHH) aryl hydrocarbon hydroxylase activity on the covalent binding of tritiated benzo(a)pyrene to rat liver DNA was evaluated in vivo. Induction of mAHH was obtained after phenobarbitone treatment (180% of control), which increased DNA binding to 210%, but left the nAHH unchanged. mAHH and nAHH were slightly induced with dieldrin (130% and 120%), but the binding remained unchanged. The increasing effect of mAHH as well as the possibly decreasing effect of nAHH induction on the binding became obvious when the data of 11 individual rats were used to solve the equation Binding = aX(mAHH) + bX(nAHH) + c. Multiple linear regression analysis resulted in positive values for a and c, a negative value for b, and a multiple correlation coefficient R = 0.82. An influence of other enzymes involved in the metabolism of benzo(a)pyrene cannot be excluded. The study shows clearly that the binding of a foreign compound to DNA in vivo is not only dependent on microsomal enzyme activities but also on nuclear activities even if the latter are considerably lower than those of microsomes.

Animals↗
PubMed1980

Benzo(a)pyrene hydroxylase from Saccharomyces cerevisiae. Substrate binding, spectral and kinetic data.

Saccharomyces cerevisiae, brewer's yeast, produces a microsomal benzo(a)pyrene hydroxylase when grown at high glucose concentrations of which the haemoprotein, cytochrome P-450 (RH, reduced-flavoprotein:oxygen oxidoreductase (RH-hydroxylating) EC 1.14.14.1) is a component. We report here kinetic data derived from Lineweaver-Burk plots of benzo(a)pyrene hydroxylation. The Michaelis constant was decreased by growth of the yeast in the presence of benzo(a)pyrene showing the induction of a form of the enzyme more specific for this compound. NADPH or cumene hydroperoxide could be used as cofactors by this enzyme, although with different Km and V values for benzo(a)pyrene. A solubilised and a solubilised, immobilised enzyme preparation were capable of benzo(a)pyrene hydroxylation, using cumene hydroperoxide but not NADPH as the cofactor. Benzo(a)pyrene was found to produce a modified type I spectral change with yeast and rat liver microsomes. The interaction of benzo(a)pyrene with cytochrome P-450 was investigated further by means of an equilibrium gel filtration technique. There appeared to be 20 binding sites per mol ofcytochrome P-450 for benz(a)pyrene, in both yeast and rat liver microsomes.

Animals↗