Studies on the utilization of inorganic pyrophosphate by different metabolic systems in yeast mitochondria

A mitochondrial pyrophosphatase (PPase) from yeast cells (Saccharomyces cerevisiae) was studied and characterized. The hydrolytic activity towards inorganic pyrophosphate (PPi) was inhibited by different SH-reagents and increased in the presence of uncouplers, indicating a possible involvement of this enzyme in energy-linked processes. This view was also supported by the observation that these mitochondria were able to hydrolyze PPi, generating an electrical membrane potential (delta psi) of the same magnitude as that obtained with ATP. Both ATP and PPi inhibited the pyruvate dehydrogenase complex and it was demonstrated that PPi can be used as substrate by mitochondrial kinases leading to the same pattern of protein phosphorylation as when ATP is used.