Competition Between Electron Transfer and ATPase in Generating Steady-State Protonmotive Force and Phosphorylation Potential

Abstract

According to current concepts of the nature of ‘tatic head’ or state 4 respiration, proton leakage (or ‘pump slippage’) will occur and this leakage will increase until a static head is reached^1–3. This energy dissipation is replenished by respiration and attendant proton pumping — arriving at a steady-state external ATP/ADP ratio (or phosphorylation potential) which cannot be exceeded due to the intrinsic dielectric constant of the membrane for charge movement. In this view the phosphorylation potential and protonmotive force are in thermodynamic equilibrium with each other. This concept is depicted in Figs. 1 and 2. In Fig. 1 is shown a classical schematic description of the oxidative phosphorylation process, where A, B, C — are adjacent members of the respiratory chain, the central box (~) is the principal energy-transducing intermediate of oxidative phosphorylation (now considered the bulk phase protonmotive force or other co-existing intermediate state) and, at the bottom is the linked reversible ATPase. Mitochondria are considered to generate a steady-state [~] in near equilibrium with a phosphorylation potential (ΔGp), depending on the velocity of energy-consuming reactions when oxidizable substrates are present in excess.