Protonmotive force in giant mitochondria

The accompanying communication [Eur. J. Biochem. 141 (1984) 1–4] indicates that the microinjection of the pH fluorescent indicator pyranine (8‐hydroxy‐1,2,6‐pyrenesulfonate) into giant mitochondria or mitoplasts does not affect their ability to carry out oxidative phosphorylation. The dye can therefore be used as a quantitative indicator of internal mitochondrial pH. We found that activation of metabolism in rotenone‐inhibited giant mitochondria by the addition of succinate produces an internal pH change corresponding to a pH shift of 0.3 to the alkaline range, approximately the same value found previously for conventional rat liver mitochondria.