Effects of preincubation invitro with 3, 4-benzopyrene and phenobarbital on the drug-metabolism systems present in the microsomal and soluble fractions of the avocado pear (Persea americana).

These findings could be interpreted as implying that the enhancement by carcinogens in vitro of hamster hepatic microsomal biphenyl 2-hydroxylase (McPherson ‘et al., 19746) is mediated through an effect on the microsomal membrane rather than via direct specific conformational modification of the biphenyl 2-hydroxylase enzyme itself. In an attempt to differentiate between the soluble and microsomal biphenyl 2and.4hydroxylase activities, the effects of classical cytochrome P-450 inhibitors such as CO and SKF 525A, and the influence of storage, metal salt inhibition and NADH on the activities of theseenzymes wereexamined and compared with those of the biphenyl hydroxylases of hamster hepatic microsomal fractions (see Table 2). From these results it is not possible to discriminate between the properties of microsomal and soluble biphenyl 2and 4-hydroxylases. Avocado-pear and hamster preparations were similar in that biphenyl 2-hydroxylation was less prone to cytochrome P-450 inhibitors than biphenyl 4-hydroxylation. Further, NADH could be satisfactorily substituted for NADPH in the 2-hydroxylation but not the 4-hydroxylation reactions. However, it was also apparent that the biphenyl 2and 4hydroxylases of the avocado pear were less prone to the effects of cytochrome P-450 inhibitors than those of the Syrian hamster. This may be attributableeither to differences in the microenvironment of the endoplasmic reticulum, or differences in the nature of cytochrome P-450 in the avocado-pear and hamster systems.