The distinct nature and function of NADPH-cytochrome c reductase and the NADPH-dependent mixed-function amine oxidase of porcine liver microsomes

Two microsomal flavoproteins, NADPH-cytochrome c reductase (EC 1.6.2.3) and a NADPH-dependent mixed-function amine oxidase, isolated from pig liver microsomes have been examined to determine if they are different enzymes or merely two different forms of a common microsomal flavoprotein. The isolated flavoproteins are different immunochemically, and with respect to their physical and enzymic properties. The isolated amine oxidase does not yield a cytochrome c reductase when treated with pancreatic lipase (used in solubilizing the cytochrome c reductase from liver). The NADPH-cytochrome c reductase and NADPH-dependent amine oxidase activities of hepatic microsomes can also be separated and recovered in separate fractions. In addition, there is an increase in cytochrome c reductase, but not in NADPH-dependent amine oxidase activity in hepatic tissue from pigs pretreated with phenobarbital. The data presented demonstrate unequivocally that the two FAD-containing enzymes, isolated and purified to homogeneity from pig liver microsomes, are distinct flavoproteins.