Components of a new mitochondrial enzyme system are being isolated. The enzyme system appears to be involved in the vectorial coupling of citrate transport through the inner mitochondrial membrane with metabolic cycles (Krebs cycle). Its components are a glutathione-citrate thiolester synthetase, utilizing the protein-glutathione mixed disulfide and citrate as substrates, a protein-sulfenic acid reductase, using reduced pyridine nucleotides as reducing agents and a protein thiol-oxidized glutathione thiol-disulfide exchange enzyme and a thiolester hydrolase. Partial purification of the entire multienzyme complex and chemical identification of individual steps were accomplished.