Studies on the Microsomal Reduced Nicotinamide Adenine Dinucleotide Phosphate-cytochrome c Reductase from Rabbit Liver

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Abstract
NADPH-cytochrome c reductase from rabbit liver microsomes was purified to a homogeneous flavoprotein with flavin adenine dinucleotide as the prosthetic group. This enzyme is reduced by either NADPH or NADH and has secondary activities as transhydrogenase and diaphorase. The NADPH-cytochrome c reductase and diaphorase activities are inhibited by NADH. The Km for NADPH of the reductase activity is 3.2×10−6M and that for NADH is 1.3×10−3M. The Km for NADPH or NADH of the diaphorase activity is essentially identical with that of the reductase activity. The Km for NADPH in the enzymatic activity of transhydrogenation between NADPH to NAD³ is 607×10−5M and the Km for NAD³of the transhydrogenase activity is 209×10−3M. The enzyme activity is inhibited by a series of quinoline derivatives and some other aromatic compounds in competition with NADPH. The extent of inhibition increases with increasing chain length of the alkyl substituents.