Biosynthesis of odd-and even-numbered cerebroside fatty acids: evidence for two routes.

Biosynthesis of the longer saturated fat ty acids can be considered to involve two steps: (I) synthesis of a primary fa t ty acid, usually palmitate, and (2) chain lengthening of the primary acid by addition of acetate moieties. The odd-numbered acids appear to be made by the same enzyme systems, starting with propionate instead of acetate at the e-end. We present here evidence that a similar pair of steps is involved in the formation of the very long acids, lignoceric (24:o*), cerebronic (24 h: o*), and their close homologs. Evidence is presented also which indicates that the 23 h :o acid, and possibly other hydroxy acids, are made by a second route, a i-carbon degradation of a longer acid. Weanling rats were given a single injection of [I-14C]acetate and groups were killed at various intervals. Cerebroside and whole brain acids were isolated from the pooled brains and the activities of most of the saturated acids were determined z. In the case of the hydroxy acids, degradation was carried out with KMnO4-acetic acid. The CO 2, from the COOH group, was collected in hyamine and the resultant shorter acid was recovered by extraction. A similar degradation was carried out on the normal (non-hydroxy) acids with NaNs-H2SO 4. Both the CO 2 and the resultant fa t ty amine were counted. Recoveries of 14C in both types of degradation were usually over 95 % and over-degradation amounted to only a few percent.