Synthesis of docosahexaenoyl coenzyme A in human spermatozoa.
The synthesis of docosahexaenoyl coenzyme A (22:6-CoA) was studied in a long-chain fatty acid: CoASH ligase (AMP)-enriched fraction from human spermatozoa and was compared to palmitoyl CoA (16:0-CoA) synthesis. The pH optimum for 22:6 activation was 8.4, which was identical to the value obtained with 16:0. The Km for ATP was 0.5 mM when 22:6 was the acyl substrate; however, when 16:0 was incubated with the ligase preparation, the Km for ATP was 2.9 mM. When CoASH was varied and 22:6 was the fatty acyl acceptor, a pattern of negative cooperatively was observed. This was confirmed by a downwardly concave double-reciprocal plot, a Hill coefficient of 0.63, and an Rs in excess of 150. The Hill coefficient with 16:0 and CoASH was 0.94. Palmitic acid was demonstrated to be a competitive inhibitor of 22:6-CoA synthesis. Based upon these data, we conclude that the kinetics of spermatozoan ligase are complex, and, in addition, these data support the hypothesis that 22:6 may regulate ligase activity, and therefore free fatty acid utilization, in sperm.
Jones
R E
RE
Department of Medicine, Madigan Army Medical Center, Tacoma, Washington.
Plymate
S R
SR
D000214:Acyl Coenzyme A / Q000096:biosynthesis*; D000255:Adenosine Triphosphate / Q000378:metabolism; D003066:Coenzyme A Ligases / Q000378:metabolism; D004789:Enzyme Activation; D006801:Humans; D008297:Male; D010171:Palmitoyl Coenzyme A / Q000096:biosynthesis; D012097:Repressor Proteins; D029701:Saccharomyces cerevisiae Proteins; D013094:Spermatozoa / Q000378:metabolism*; D000098859:Long-Chain-Fatty-Acid-CoA Ligase
D000214:Acyl Coenzyme A; D012097:Repressor Proteins; D029701:Saccharomyces cerevisiae Proteins; C044663:docosahexaenoyl-coenzyme A; D010171:Palmitoyl Coenzyme A; D000255:Adenosine Triphosphate; D003066:Coenzyme A Ligases; C090799:FAA2 protein, S cerevisiae; D000098859:Long-Chain-Fatty-Acid-CoA Ligase