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

  • Woods L
  • Wiseman A
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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 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 cumune hydroperoxide could be used as cofactors by this enzyme, although with different Kmand 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 of cytochrome P-450 for benzo(a)pyrene, in both yeast and rat liver microsomes. © 1980.

Author-supplied keywords

  • (S. cerevisiae)
  • Benzo(a)pyrene hydroxylase
  • Cytochrome P-450
  • Substrate binding

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  • Leonard F J Woods

  • Alan Wiseman

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