Substrate specificity of fatty-acyl-CoA ligase in liver microsomes.

The substrate specificity of fatty-acyl-CoA ligase in liver microsomes has been studied in a system in which fatty acids are present initially as complexes with unilamellar vesicles of phosphatidylcholine. The latter were prepared by cosonication of phospholipids and different fatty acids. As compared with previous studies of the enzyme the activity of acyl-CoA ligase is several-fold higher for assays carried out with fatty acid substrates added as components of a bilayer. This was true for all fatty acids studied. Also as compared with data reported previously in the literature there was a systematic relationship between the structure of fatty acids, activity at Vmax for synthesis of acyl-CoA and avidity of binding to the ligase. Activity at Vmax was greatest for lauric acid and decreased with increasing chain length. The apparent avidity of enzyme for fatty acids was greatest for octanoic acid and decreased as chain length increased.