Acyl-CoA synthetase in oilseeds: fatty acid structural requirements for activity and selectivity
1997
Ichihara, K. | Yamane, K. | Hiraon, E.
The substrate specificities and selectivities of acyl-CoA synthetases from maturing oilseeds were investigated to reveal fatty acid structures that the enzymes recognize. The synthetases from rapeseed (Brassica napus) and castor bean (Ricinus communis) activated palmitic acid 16:0 most rapidly among the saturated fatty acids tested. Native unsaturated fatty acids, oleic 18:1 cis-9, linoleic 18:2 cis-9,12 and linolenic acid 18:3 cis-9,12,15, were all effectively utilized. Palmitoleic acid 16:1 cis-9 was also a good substrate, while myristoleic acid 14:1 cis-9 was a poor substrate. The activation of erucic acid 22:1 cis-13 was very slow. Elaidic acid 18:1 trans-9 was utilized at rates similar to those of the cis isomer. The efficiencies of petroselinic acid 18:1 cis-6 were half the efficiencies of oleic acid, while the rates of activation of cis-vaccenic acid 18:1 cis-11 were comparable to those for oleic acid. These findings suggest that acyl-CoA synthetases of oilseeds producing long-chain fatty acids strictly recognize the molecular structures of fatty acids, i.e., the carbon-chain length between C16-C18 and the position of the first double bond (pi electrons) between delta9-delta 11. The castor bean and safflower (Carthamus tinctorius) enzymes were selective for linoleic and oleic acids over palmitic and stearic acids, whereas the specific activities of these enzymes for palmitic acid were similar to those for oleic acid. It was thus revealed that the selectivity of acylCoA synthetase for fatty acid molecular species does not exactly reflect the specificity.
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