Chain Elongation, 2-Hydroxylation, and Decarboxylation of Long Chain Fatty Acids by Yeast

Chain elongation and 2-hydroxylation pathways, which are specific for very long chain fatty acids (gC18), have been found in the yeast, Candida utilis. The chain elongation system acts specifically on fatty acids of chain length C20 to C24; there is no detectable elongation of C18 and only trace activity with C19. The product of the elongation enzyme or enzymes is C26 when C20, C22, or C24 is substrate and is a mixture of C25 and C27 when the substrates are C21 and C23. The 2-hydroxylation enzyme converts C26 acid, formed in situ by chain elongation, to 2-hydroxyhexacosanoic acid. The enzyme seems quite specific for the C26 chain length, although there may be some activity for chain lengths C24, C25, and C27. In addition to the chain elongation and 2-hydroxylation systems, a relatively nonspecific system for the oxidative decarboxylation of 2-hydroxy acids has been studied in C. utilis. All 2-hydroxy fatty acids tested (C18 through C26 containing an even number of carbons) were converted, in part, to the unsubstituted acid containing 1 carbon less than the substrate. Decarboxylation was most efficient with 2-OH-C18 and least with 2-OH-C26 acids. Another product arising from the decarboxylation reaction was the aldehyde containing 1 carbon less than the 2-hydroxy acid substrate. The aldehydes were detected in trace amounts with the shorter chain substrates but were major products from the decarboxylation of 2-OH-C24 and 2-OH-C26. Presumably, the aldehyde is an intermediate between the 2-hydroxy acid substrate and the unsubstituted fatty acid which results as the final product in the oxidative decarboxylation process.