The induction of cytochrome P-448 dependent benzo(a)pyrene hydroxylase in |
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Authors: | David J. King Mahmood R. Azari Alan Wiseman |
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Affiliation: | Biochemistry Division, Department of Biochemistry, University of Surrey, Guildford, Surrey, U.K. |
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Abstract: | When grown in high concentrations of glucose, the yeast produces a microsomal cytochrome P-450 monooxygenase system which is capable of hydroxylating benzo(a)pyrene. The addition of benzo(a)pyrene to the yeast during growth causes only a small increase in cytochrome P-448 levels but results in a dramatic improvement in the apparent kinetics of benzo(a)pyrene hydroxylation as measured by a decrease in the Michaelis constant and an increase in maximal velocity. Dimethylnitrosamine, phenobarbital and 3-methylcholanthrene also induce this enzyme to various degrees. Yeast pretreatment with β-naphthoflavone did not affect this enzyme, yet pretreatment with lanosterol resulted in a decreased affinity for benzo(a)pyrene. The addition of benzo(a)pyrene to yeast growing at low glucose concentration does not induce cytochrome P-448. The implications of these findings with regard to the presence of multiple forms of cytochromes in yeast are briefly discussed. |
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