SYNTHESIS AND HYDROLYSIS OF LONG-CHAIN FATTY ACYL-COENZYME-A THIOESTERS BY SOLUBLE AND MICROSOMAL FRACTIONS FROM BRAIN OF DEVELOPING RAT

The specific activities of long-chain fatty acid-CoA ligase (EC 6.2.1.3) and of long-chain fatty acyl-CoA hydrolase (EC 3.1.2.2) were measured in soluble and microsomal fractions from rat brain. In the presence of either palmitic acid or stearic acid, the specific activity of the ligase increased during development; the specific activity of this enzyme with arachidic acid or behenic acid was considerably lower. The specific activities of palmitoyl-CoA hydrolase and of stearoyl-CoA hydrolase in the microsomal fraction decreased markedly (75%) between 6 and 20 days after birth; by contrast, the corresponding specific activities in the soluble fraction showed no decline. Stearoyl-CoA hydrolase in the microsomal fraction was inhibited (99%) by bovine serum albumin; in contrast with the microsomal fatty acid-chain-elongation system, which was stimulated 3.9-fold by albumin. Inhibition of stearoyl-CoA hydrolase did not stimulate stearoyl-CoA chain elongation. Therefore the decline in the specific activity of hydrolase during myelogenesis probably is not responsible for the increased rate of fatty acid chain elongation. The decline in specific activity of the microsomal hydrolase and to a lesser extent the increase in the specific activity of the ligase may be directly related to the increased demand for long-chain acyl-CoA esters during myelogenesis as substrates in the biosynthesis of myelin lipids.