Acyl-CoA Synthetase in Oilseeds: Fatty Acid Structural Requirements for Activity and Selectivity

The substrate specificities and selectivities of acyl-CoA synthetasesfrom maturing oilseeds were investigated to reveal fatty acidstructures that the enzymes recognize. The synthetases fromrapeseed (Brassica nap us) and castor bean (Ricinus communis)activated palmitic acid 16:0 most rapidly among the saturatedfatty acids tested. Native unsat-urated fatty acids, oleic 18:1cis-9, linoleic 18:2 cis-9,12 and linolenic acid 18:3 m-9,12,15,were all effectively utilized. Palmitoleic acid 16:1 cis-9 wasalso a good substrate, while myristoleic acid 14:1 cis-9 wasa poor substrate. The activation of erucic acid 22:1 cis-13was very slow. Elaidic acid 18:1 trans-9 was utilized at ratessimilar to those of the cis isomer. The efficiencies of petroselinicacid 18:1 cis-6 were half the efficiencies of oleic acid, whilethe rates of activation of m-vaccenic acid 18:1 cw-11 were comparableto those for oleic acid. These findings suggest that acyl-CoAsynthetases of oilseeds producing long-chain fatty acids strictlyrecognize the molecular structures of fatty acids, i.e., thecarbon-chain length between C¹⁶-C¹⁸ and the position of thefirst double bond (