EFFECT OF STORAGE OF FROZEN LIVER MICROSOMAL PREPARATIONS ON HYDROXYLATION OF TESTOSTERONE AND PENTOBARBITAL AND N-DEMETHYLATION OF ETHYLMORPHINE

The activity of the liver microsomal enzyme systems responsible for the hydroxylation of testosterone in the 7α-, 16α- and 6β-positions is differentially affected by storage of microsomal preparations at -15°. The 16α-hydroxylase activity decreased upon storage of microsomal suspensions or lyophilized preparations for 20 days, but was not affected when the microsomes were stored as a pellet. In contrast, the 7α- hydroxylase activity remained essentially unchanged while the 6β-hydroxylase activity decreased in all three microsomal preparations. The stability of pentobarbital hydroxylase and ethylmorphine N-demethylase was similar to that obtained for testosterone 16α-hydroxylase. The differential effects of storage of liver microsomal preparations on the hydroxylation of testosterone in the 6β-, 7α- and 16α-positions suggest that a single cytochrome cannot alone determine the specificity of the three hydroxylation reactions. In addition, the results suggest that when storage of microsomes for more than 1 day is absolutely necessary, microsomes should be stored as a pellet rather than as a suspension or as a lyophilized powder. © 1969.