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

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NADYH-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 K_m for NADPH of the reductase activity is 3.2×10^-6M and that for NADH is 1.3×10^-3M. The K_m for NADPH or NADH of the diaphorase activity is essentially identical with that of the reductase activity. The K_m for NADPH in the enzymatic activity of transhydrogenation between NADPH to NAD⁺ is 6.7×10^-6M and the K_m for NAD⁺ of the transhydrogenase activity is 2.9×10^-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.