FATTY-ACID STRUCTURAL REQUIREMENTS FOR ACTIVITY OF ARACHIDONOYL-COA SYNTHETASE

  • 1 January 1984
    • journal article
    • research article
    • Vol. 25  (3) , 288-293
Abstract
The fatty acid substrate specificity of arachidonoyl-CoA synthetase from human platelet membranes were examined. A variety of positional isomers and chain-length analogs of arachidonic acid [20:4(5, 8, 11, 14)] were synthesized, and assayed for their ability to inhibit arachidonoyl-CoA formation or to serve as substrates for the synthetase. The chain-length specificity of the synthetase for .DELTA.8,11,14 trienoic fatty acids was C19 > C18 = C20 .mchgt. C21 > C22. Inhibition activity by positional isomers of arachidonate was 20:4(5, 8, 11, 14) .simeq. 20:4(6, 9, 12, 15) = 20:4(7, 10, 13, 16) .mchgt. 20:4(4, 7, 10, 13), however, Vmax for arachidonate was greater than that for 20:4(6, 9, 12, 15). The enzyme apparently counts double bonds from the carboxyl terminus. As counted from the methyl terminus several n-6, -9, -12 fatty acids were ineffective as inhibitors [18:3(6, 9, 12); 19:4(4, 7, 10, 13); 21:3(9, 12, 15)], whereas all methylene-interrupted tri- and tetraenoic fatty acids which contained .DELTA.8 and .DELTA.11 double bonds were potent inhibitors. The .DELTA.11 double bond was best associated with optimal inhibition: 20:3(5, 11, 14) had a lower Ki than 20:3(5, 8, 14). 13-Methyl-20:3(8, 11, 14) did not inhibit the enzyme. Partially purified enzyme from calf brain, depleted of nonspecific long-chain acyl-CoA synthetase, exhibited the same fatty acid specificity as crude platelet enzyme.