Fatty acid metabolism in the microsomal fraction of developing rabbit brain.

1. Incorporation of [14C]malonyl-CoA into fatty acid and lipid by the microsomal fraction from developing rabbit brain has been determined. 2. The specific activity for malonyl-CoA incorporation into preformed fatty acid reached a maximum at 15-20 days of age and the increase in enzyme activity paralleled that of palmitoyl-CoA synthesis in the microsomal fraction. 3. Most of the preformed fatty acid was derived from microsomal membrane lipid, and added acyl-CoA only slightly increased the incorporation. Inhibition occurred at concentrations in excess of 2 muM acyl-CoA. Endogenous acyl-CoA may be formed by acyl-group turnover through the action of phospholipase A and acyl-CoA synthetase. 4. Added 14C-labelled acyl-CoA was elongated to a longer chain-length product than endogenous fatty acid elongated with [14C]malonyl-CoA. 5. Both ATP and acyl-CoA influence the incorporation of elongated fatty acids into complex lipids, possibly through their effect on acyl-CoA synthetase.