[Catalytic properties of monooxygenases from isolated immunocompetent cells].

The kinetic parameters of two monoxygenase (N-demethylase and benzo(a)pyrene hydroxylase) reactions occurring in murine immunocompetent cells were determined. It was shown that the pH optimum for macrophage enzymes lies at 7.4, whereas that for thymocytes and spleen cells at 8.5. The effects of cytochrome P-450 inhibitors (methyrapone, SKF-525A, tilorone) on monooxygenase systems of immunocytes were investigated. Methyrapone and SKF-525A were shown to be effective inhibitors of N-demethylase. The mode of inhibition changes from non-competitive to competitive, depending on the inhibitor concentration. Tilorone, an immunostimulator and inhibitor of liver cytochrome P-450-dependent enzymes, competitively inhibits N-demethylase and benzo(a)pyrene hydroxylase of immunocytes.