UNIDIRECTIONAL ARGININE TRANSPORT IN RECONSTITUTED PLASMA-MEMBRANE VESICLES FROM YEAST OVEREXPRESSING CAN1

Amino acids are accumulated in Saccharomyces cerevisiae by strictly unidirectional influx systems. To see whether cellular compartmentation causes this unusual amino-acid-transport behaviour, arginine transport was studied in plasma-membrane vesicles. The arginine permease gene CAN1 was overexpressed in S. cerevisiae RH218a and in a permease-deficient mutant RS453 (can1). Reconstituted plasma-membrane vesicles from these transformants, energized by incorporated cytochrome-c oxidase, showed 3-4-fold increased rates of arginine uptake compared to vesicles from wild-type cells. The K(T) values were 32.5 muM in vesicles from wild-type and 28.6 muM in vesicles from transformed cells; the corresponding in vivo values were 17.5 muM and 11.4 muM, respectively. It could be demonstrated that unidirectional arginine transport and accumulation also exist in vesicles; thus, unidirectional influx is not related to cellular compartmentation.