title: Alpha reduced nicotinamide adenine dinucleotide-dependent reductase reactions of rat liver microsomes.
abstract: The kinetics of alpha-NADH-dichlorophenolindophenol (DCPIP) and alpha-NADH-cytochrome c reductase reactions of rat liver microsomes showed that the reactio ns proceeded by a ping-pong mechanism, and that the oxidation of alpha-NADH was the rate-determining reaction. The DCPIP-reducing activity with alpha-NADH in the presence of ADP was about 1% of that with beta-NADH. ADP inhibited the alpha-NADH-DCPIP reductase reaction in a competitive manner with respect to alpha-NADH and a value of 1.2 mM  for the inhibition constant was obtained. ADP also inhibited cytochrome b5 reduction with alpha-NADH. More than 90% of cytochrome b5 was reduced under conditions where 90% of the alpha-NADH-DCPIP reductase activity was suppressed with ADP. The reduction of DCPIP with alpha-NADH preceded that of cytochrome b5, but the reductions partly overlapped. From these results, a diversed electron flow from alpha-NADH to cytochrome b5 and electron sharing between cytochrome b5 and DCPIP were indicated. alpha-NAD+ also inhibited the alpha-NADH-DCPIP reductase reaction. Analyses of the inhibition indicated that two types of alpha-NADH-DCPIP reductase reaction existed, one of which was resistant to alpha-NAD+ inhibition. In contrast to the reoxidation of beta-NADH-reduced cytochrome b5, the process was largely monophasic when cytochrome b5 was reduced with alpha-NADH.
mesh_terms: D015086:2,6-Dichloroindophenol / Q000378:metabolism; D000244:Adenosine Diphosphate / Q000494:pharmacology; D000818:Animals; D003580:Cytochromes / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D007700:Kinetics; D008297:Male; D008862:Microsomes, Liver / Q000201:enzymology*; D009243:NAD / Q000494:pharmacology; D009247:NADH, NADPH Oxidoreductases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D009251:NADPH-Ferrihemoprotein Reductase / Q000378:metabolism; D051381:Rats; D013237:Stereoisomerism
chemical_list: D003580:Cytochromes; D009243:NAD; D000244:Adenosine Diphosphate; D015086:2,6-Dichloroindophenol; D009247:NADH, NADPH Oxidoreductases; D009251:NADPH-Ferrihemoprotein Reductase