Phosphatase affects microsomal monooxygenase mainly via reductase.

Treatment with alkaline phosphatase of hepatic microsomes prepared from rabbit, rat, and mouse caused a marked decrease of their specific monooxygenase activity (7-ethoxycoumarin-deethylation). This decrease occurred without a significant change in the microsomal content of cytochrome P-450, but with an equally marked decrease of NADPH-cytochrome P-450 reductase (cytochrome c reduction). Thus the phosphatase effect on monooxygenase is mainly due to the inactivation of the reductase.