Synthesis of Docosahexaenoyl Coenzyme A in Human Spermatozoa

Abstract

ABSTRACT 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 cooperativity 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.