STUDIES ON THE UTILIZATION OF INORGANIC PYROPHOSPHATE BY DIFFERENT METABOLIC SYSTEMS IN YEAST MITOCHONDRIA

A mitochondrial pyrophosphatase (PPase) from yeast cells (Saccharomyce s cerevisiae) was studied and characterized. The hydrolytic activity t owards inorganic pyrophosphate (PPi) was inhibited by different SH-rea gents and increased in the presence of uncouplers, indicating a possib le involvement of this enzyme in energy-linked processes. This view wa s also supported by the observation that these mitochondria were able to hydrolyze PPi, generating an electrical membrane potential (DELTAPS I) of the same magnitude as that obtained with ATP. Both ATP and PPi i nhibited the pyruvate dehydrogenase complex and it was demonstrated th at PPi can be used as substrate by mitochondrial kinases leading to th e same pattem of protein phosphorylation as when ATP is used.