Acid:Coenzyme A Ligase in Brain: Fatty Acid Specificity in Cellular and Subcellular Fractions

Abstract

Long-chain fatty acid:coenzyme A (CoA) ligase (EC 6.2.1.3) activity with 4 fatty acids was measured in rat brain homogenates and cellular and subcellular fractions to determine whether there are differences in activity that could be correlated with differences in fatty acid composition and metabolism. In rat brain homogenates, ligase activity varied appreciably with the 4 acids, with 18:2 > 18:1 > 16:0 > 22:1 (nmol acyl-CoA formed/min/mg protein; 1.46, 1.20, 0.96 and 0.57, respectively). This order was similar under all incubation conditions tested, including variable pH and fatty acid concentrations. The relative specific activities (RSA, 16:0 = 1.0) with the 4 substrates were similar in rat brain homogenate, mitochondria and microsomes, with the highest specific activities in the latter fraction. The RSA were also similar in ox brain homogenates, in rabbit brain microsomes prepared from gray and white matter, in neurons isolated from rat brain and in cultured neuroblastoma cells. Rat liver homogenates had a significantly different pattern of RSA. The ligase(s) apparently has a preference for certain fatty acids, but the major control of fatty acid composition and metabolism is probably a function of subsequent metabolic steps.