A biosynthetic role for carnitine in the yeast Torulopsis bovina.

The mode of action of carnitine on the growth of the yeast Torulopsis bovina ATCC 26014 was investigated. When 0.5-5 microM L-carnitine was added to the medium, the growth rate doubled for both aerobic and anaerobic cultures. Cells grown in the absence of carnitine contain 0.4 nmol of L-carnitine/g, wet weight, but with 5 microM L-carnitine in the media, cells contain 1400 nmol of carnitine/g, wet weight, by the end of exponential growth. When [1-14C]acetyl-L-carnitine was added to growth media, almost all of the radioactivity became cell-associated. Most of the 14C was incorporated into cell protein although considerable 14C was recovered in the fatty acid fraction of saponified cells. Analyses of the amino acids derived from radiolabeled protein showed that the acetyl[14C] of acetylcarnitine was in glutamate, arginine, proline, leucine, and lysine. In contrast, [1-14C]acetate labeled leucine and lysine. Isopycnic density gradient analysis demonstrated that carnitine acetyltransferase was primarily associated with mitochondria, while acetyl-CoA synthetase and acetyl-CoA hydrolase were cytosolic. Isolated mitochondria incorporated [14C]acetylcarnitine radioactivity into citrate and 2-oxoglutarate. The data are consistent with carnitine facilitating the transfer of acetyl groups from the cytosol into mitochondria for synthesis of citrate and its metabolites. These results demonstrate a role for carnitine in biosyntheses in the yeast T. bovina.