Evidence for a second microsomal trans-2-enoyl coenzyme A reductase in rat liver. NADPH-specific short chain reductase.
Evidence for the existence of a previously unknown rat hepatic microsomal reductase, short chain trans-2-enoyl-CoA reductase (SC reductase) is presented. This reductase has a specific requirement for NADPH, is unable to utilize NADH, and catalyzes the conversion of crotonyl-CoA and trans-2-hexenoyl-CoA to butyric acid and hexenoic acid at a rate of 5 and 65 nmol per min per mg of microsomal protein, respectively. Highly purified NADPH cytochrome P-450 reductase incorporated into liposomes prepared from dilauroyl phosphatidylcholine in the presence or absence of cytochrome P-450 possesses no SC reductase activity. These liposomal preparations did, however, catalyze mixed function oxidations of benzphetamine and testosterone. Rabbit antibody to rat liver NADPH cytochrome P-450 reductase had little to no effect on the conversion of crotonyl-CoA and trans-2-hexenoyl-CoA, suggesting that the SC reductase accepts reducing equivalents directly from NADPH. When acetoacetyl-CoA was incubated with hepatic microsomes and either NADH or NADPH, no formation of butyrate was detected; however, when both cofactors were present, a rate of formation of 3 nmol of butyrate was determined per min per mg of microsomal protein. These results suggest the presence of a previously unknown short chain beta-ketoreductase which catalyzes the reduction of short chain beta-keto acids, only in the presence of NADH. Our results also indicate that the electrons from NADH to the beta-ketoreductase bypass cytochrome b5. The physiological significance is discussed in terms of lipogenesis and ketone body utilization by the liver.
D000818:Animals; D044943:Fatty Acid Desaturases / Q000302:isolation & purification* / Q000378:metabolism; D064429:Fatty Acid Synthases; D007106:Immune Sera; D007700:Kinetics; D008297:Male; D008862:Microsomes, Liver / Q000201:enzymology*; D009247:NADH, NADPH Oxidoreductases; D009249:NADP; D009251:NADPH-Ferrihemoprotein Reductase / Q000302:isolation & purification / Q000378:metabolism; D010084:Oxidation-Reduction; D051381:Rats; D011919:Rats, Inbred Strains
D007106:Immune Sera; D009249:NADP; D044943:Fatty Acid Desaturases; C036543:short chain trans-2-enoyl-CoA reductase; D009247:NADH, NADPH Oxidoreductases; D009251:NADPH-Ferrihemoprotein Reductase; D064429:Fatty Acid Synthases