The activities of aryl hydrocarbon hydroxylase and 7-ethoxycoumarin O-de-ethylase in the rat submandibular gland, both of which are normally very low, were increased about 10- and 25-fold, respectively, by administration of 3-methylcholanthrene. The increased activity of aryl hydrocarbon hydroxylase was inhibited by 7,8-benzoflavone but little if any by metyrapone and SKF-525A. The submandibular gland aryl hydrocarbon hydroxylase was also inhibited by antibodies elicited against rat liver cytochrome P-448 and NADPH-cytochrome P-450 reductase, respectively, and slightly by anti-cytochrome b5 antibody, suggesting that submandibular gland aryl hydrocarbon hydroxylase resembles that of the liver, not only in the immunochemical properties of cytochrome P-450 involved, but also in the entire enzyme complex, including the electron transferring system. Cofactor(s) required by aryl hydrocarbon hydroxylase in submandibular gland was NADPH, whereas NADH sustained the reaction at a much slower rate (about 20%). NADH showed some additive action when added with NADPH.
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