Requirement of a soluble protein for maximal activity of the mono-oxidase system of hepatic microsomes

Abstract

Hepatic microsomes were shown to possess only about 1 3 to 1 2 of the aminopyrine and ethylmorphine (EM) N-demethylase activities of the 9000 × g supernatant fraction from which they were derived. Activity was restored with the 105,000 × g supernatant fraction (SF). The factor in SF is heat labile, precipitated by ammonium sulfate or acetone, none-dializable, and resists sedimentation at 170,000 × g for 4 hr. SF elevated the K m for EM N-demethylation. These observations suggest that the factor in SF is a macromolecule which functions as an unknown component of the monoxidase system, as an activator of the system, or by removing an inhibitor of the system.