Compartmentation of the amino acid pool in Saccharomycopsis lipolytica.

1. The size of the free amino acid pool in S. lipolytica varies from 250 to 350 micronmoles/g dry wt., and it accounts for about 10% of the total amino acid content; 80-90% of free amino acids, including methionine, is compartmentized in vacuole. S-Adenosylmethionine (SAM) occurs in equal proportions in vacuole and cytoplasm while aspartate and glutamate are mainly cytosolic. 2. The bulk of the methionine overproduced in the ethionine-resistant mutant Etr-13, and of the exogenous methionine derived from the methionine-enriched medium, is stored in vacuole. The amount and distribution of SAM is not affected. 3. Overloading with endogenous methionine results in a significant increase in the total cytosolic amino acid pool and is associated with the increased concentration of arginine, glutamine and lysin; on overloading with exogenous methionine, only lysine is elevated.