The measurement of changes in pH associated with electrochemically driven respiration in rat liver mitochondria

Using an optically transparant thin layer electrode, it has been possible to measure the pH changes associated with the electrochemical turnover of horse heart cytochrome c in the presence of rat liver mitochondria and oxygen. Direct electrochemistry of cytochrome c at a gold electrode modified with bis(4-pyridyl)bisulfide allowed electron flux (current) to be measured simultaneously with the differential change in absorbance associated with phenol red, a pH-sensitive dye. Although the alkalinization due to the reduction of oxygen to water was readily observed, any initial acidification associated with proton pumping was not detected. It is suggested that at the high ratios of oxidized-to-reduced cytochrome c present during the steady state attained, proton pumping may be absent or more localized.