CANDIDA-LIPOLYTICA MUTANTS DEFECTIVE IN AN ACYL-COENZYME-A SYNTHETASE - ISOLATION AND FATTY-ACID METABOLISM

Mutant strains of C. lipolytica defective in an acyl-CoA synthetase [acid:CoA ligase (AMP-forming); EC 6.2.1.3] were isolated. The mutant strains apparently exhibited no acyl-CoA synthetase activity in vitro and were, in contrast to the wild-type strain, incapable of growing in the presence of exogenous fatty acid when cellular synthesis de novo of fatty acid was blocked. However, the mutant strains grew on either fatty acid or n-alkane as a sole C source at rates comparable to that observed for the wild-type strain. Analysis of the fatty acid composition of the lipids from the mutant cells grown on odd-chain-length fatty acid as well as [14C]oleic acid incoporation studies showed that the mutant cells, unlike the wild-type cells, cannot incorporate exogenous fatty acid as a whole into cellular lipids, but utilize the fatty acid that is synthesized de novo from acetyl-CoA produced by degradation of exogenous fatty acid. This finding indicates the presence of at least 2 acyl-CoA synthetases that activate long-chain fatty acid. One, designated acyl-CoA synthetase I, which is absent in the mutant strains, is responsible for production of acyl-CoA to be utilized for the synthesis of cellular lipids. The other acyl-CoA that is exclusively degraded via .beta.-oxidation to yield acetyl-CoA.