Evidence for a second microsomal trans-2-enoyl coenzyme A reductase in rat liver. NADPH-specific short chain reductase

• Published in: The Journal of biological chemistry 1982-12, Vol.257 (23), p.14333-14340
• Main Authors: Cinti, D L, Nagi, M N, Cook, L, White, R E
• Format: Article
• Language: English
• Subjects: Animals; Fatty Acid Desaturases - isolation & purification; Fatty Acid Desaturases - metabolism; Fatty Acid Synthases; Immune Sera; Kinetics; Male; Microsomes, Liver - enzymology; NADH, NADPH Oxidoreductases; NADP; NADPH-Ferrihemoprotein Reductase - isolation & purification; NADPH-Ferrihemoprotein Reductase - metabolism; Oxidation-Reduction; Rats; Rats, Inbred Strains
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1016/S0021-9258(19)45385-4

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.