This paper describes the problems of measuring the allosteric ATP-inhibition of cytochrome c oxidase (CcO) in isolated mitochondria. Only by using the ATP-regenerating system phosphoenolpyruvate and pyruvate kinase full ATP-inhibition of CcO could be demonstrated by kinetic measurements. The mechanism was proposed to keep the mitochondrial membrane potential (ΔΨm) in living cells and tissues at low values (100-140mV), when the matrix ATP/ADP ratios are high. In contrast, high ΔΨm values (180-220mV) are generally measured in isolated mitochondria. By using a tetraphenyl phosphonium electrode we observed in isolated rat liver mitochondria with glutamate plus malate as substrates a reversible decrease of ΔΨm from 233 to 123mV after addition of phosphoenolpyruvate and pyruvate kinase. The decrease of ΔΨm is explained by reversal of the gluconeogenetic enzymes pyruvate carboxylase and phosphoenolpyruvate carboxykinase yielding ATP and GTP, thus increasing the matrix ATP/ADP ratio. With rat heart mitochondria, which lack these enzymes, no decrease of ΔΨm was found. From the data we conclude that high matrix ATP/ADP ratios keep ΔΨm at low values by the allosteric ATP-inhibition of CcO, thus preventing the generation of reactive oxygen species which could generate degenerative diseases. It is proposed that respiration in living eukaryotic organisms is normally controlled by the ΔΨm-independent "allosteric ATP-inhibition of CcO." Only when the allosteric ATP-inhibition is switched off under stress, respiration is regulated by "respiratory control," based on ΔΨm according to the Mitchell Theory. © 2010 Elsevier B.V.
Ramzan, R., Staniek, K., Kadenbach, B., & Vogt, S. (2010). Mitochondrial respiration and membrane potential are regulated by the allosteric ATP-inhibition of cytochrome c oxidase. Biochimica et Biophysica Acta - Bioenergetics, 1797(9), 1672–1680. https://doi.org/10.1016/j.bbabio.2010.06.005