Inorganic Pyrophosphate Gives a Membrane Potential in Yeast Mitochondria, as Measured with the Permeant Cation Tetraphenylphosphonium

Evidence for a membrane potential (ΔΨ) generating capacity of inorganic pyrophosphate (PPi) with inorganic pyrophosphatase in mitochondria from the yeast Saccharomyces cerevisiae is presented. Addition of PPi increases the accumulation of the permeant cation tetraphenylphosphonium (TTP+) in mitochondria, as measured with a TPP+-selective electrode or using [3H]TPP+. This accumulation is strongly inhibited by the uncoupler carbonyl cyanide p-trifluoromethoxyphenylhydrazone (FCCP) but not by oligomycin, whereas accumulation of TPP+ induced by ATP is strongly inhibited by both FCCP and oligomycin. The values of ΔΨ obtained upon addition of PPi were similar to those obtained when yeast mitochondria were energized by NADH or ATP. Energization of the wild type yeast mitochondria with ATP resulted in higher ΔΨ values than those achieved when PPi was hydrolyzed, whereas the effect of PPi was more pronounced in mitochondria from a pyrophosphatase (PPase) overproducing yeast strain. These results clearly indicate that PPi is significant as an energy donor and that the yeast mitochondrial PPase, the gene for which we have recently cloned and sequenced, may perticipate on energy transfer reactions.