Cooperation between enzyme and transporter in the inner mitochondrial membrane of yeast. Requirement for mitochondrial citrate synthase for citrate and malate transport in Saccharomyces cerevisiae.

We have characterized 1,2,3-benzenetricarboxylic acid-sensitive, mersalyl-insensitive citrate uptake by mitochondria from two strains of Saccharomyces cerevisiae by describing the time course, Km and Vmax values, pH dependence, and response to inhibitors. In unloaded mitochondria from PSY142 CS1- cells, a mutant that lacks mitochondrial citrate synthase, both citrate uptake and efflux were reduced 7- and 8-fold, respectively, compared with the parental strain. No malate uptake was detectable in mitochondria from CS1- cells, while in the parental strain, uptake was 5.4 nmol/min/mg of protein. In contrast, mutations in peroxisomal citrate synthase (CS2-) or in other tricarboxylic acid cycle enzymes did not result in changes in mitochondrial citrate transport, suggesting a specific functional role for mitochondrial citrate synthase in citrate transport. More important, liposomes containing protein extracts from CS1- mitochondria showed the same citrate and malate transport rates as liposomes made from protein extracts of parental strain mitochondria. Thus, an apparently normal amount of both the citrate transporter and the dicarboxylate carrier is present in CS1- mitochondria, but both function abnormally in undisrupted mitochondria. We suggest that cooperation between the citrate transporter and mitochondrial citrate synthase is necessary for normal function of the transporter.