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, mersa lyl-insensitive citrate uptake by mitochondria from two strains of Sac charomyces cerevisiae by describing the time course, K-m and V-max val ues, pH dependence, and response to inhibitors. In unloaded mitochondr ia 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 st rain, 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 trans port, suggesting a specific functional role for mitochon- drial citrat e 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 pare ntal strain mitochondria. Thus, an apparently normal amount of both th e citrate transporter and the dicarboxylate carrier is present in CS1( -) mitochondria, but both function abnormally in undisrupted mitochond ria. We suggest that cooperation between the citrate trans porter and mitochondrial citrate synthase is necessary for normal function of the transporter.