Studies on the mechanism of fatty acid synthesis V. Bicarbonate requirement for the synthesis of long-chain fatty acids

Abstract

The synthesis of long-chain fatty acids from acetyl CoA is catalyzed by two highly purified enzyme fractions from avian liver in the presence of ATP, Mn ++, HCO 3 − and TPNH. DPNH can replace TPNH although the rate of fatty acid synthesis is much less. The requirement for HCO 3 − applies to synthesis not only in the purified enzyme system but also in the unfractionated extracts of pigeon liver and rat liver. H 14CO 3 − does not become incorporated into long-chain fatty acids during active synthesis from unlabelled acetyl CoA. The two enzyme fractions contain very little or none of the enzymes of the fatty acid-oxidation sequence. The TPNH-dependent α-β unsaturated acyl CoA reductase—a key enzyme in the elongation of the fatty acid chain by the reversal of β-oxidation—cannot be detected in the purified system.