Fatty acid synthesis by extracts of Euglena. II

Abstract

Fatty acid synthesis by extracts of Euglena shows an absolute requirement for ATP when acetyl-SCoA is the substrate. Since the system is not inhibited by avidin and is not enhanced by HCO 3 −, it is suggested that the malonyl-SCoA pathway is inoperative in these extracts. This conclusion is supported by the fact that the rate of incorporation of acetyl-SCoA is approximately 50-fold greater than that of malonyl-SCoA. Stoichiometric studies on ATP, NADH, 2 2 Abbreviations used: NADPH, nicotinamide-adenine dinucleotide phosphate, reduced; NADH, nicotinamide-adenine dinucleotide, reduced; NADP and NAD, oxidized forms of NADPH and NADH, respecitvely; FASF, fatty acid synthesizing fraction. and NADPH per acetyl-SCoA incorporated reveal that 1 ATP per 2 NADH and NADPH are utilized per acetyl-SCoA incorporated into long-chain fatty acids. Of the fatty acids labeled, about 60–70% of the total radioactivity in the fatty acids is distributed in fatty acids of 16–20 carbon atoms. This distribution of products was found to be independent of duration of assay.