Abstract

Benzpyrene injection in rats is associated with changes in the pH optimum of the hepatic microsomal metabolism in vitro of aniline to p-aminophenol. The shift in pH optimum (upwards from pH 7.0 in controls to as high as pH 8.0 in microsomes from benzpyrene-treated rats) was dependent on substrate concentration; low substrate concentrations totally obscured this change in pH optimum. Phospholipase C treatment in vitro of hepatic microsomes from control rats resulted in a shift in pH optimum of aniline p-hydroxylation similar to that produced by benzpyrene injections ( in vivo). Adding hexobarbital to microsomes from control rats also displaced upward the pH optimum of microsomal aniline p-hydroxylation in vitro. Taken together with some proposals and results of others, the present studies lead to the conclusion that the microsomal type I substrate-binding site is involved in determining the pH optimum of a type II substrate (aniline) of the microsomal mixed function oxidase system.

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