Thermodynamics of oxidative phosphorylation in bovine heart submitochondrial particles

The rates of both forward and reverse electron transfer in phosphorylating submitochondrial particles from bovine heart can be controlled by the thermodynamic phosphorylation potential (deltaGp) of the adenine nucleotide system. deltaGp is the Gibbs free energy of ATP synthesis and is defined by the relationship deltaGp = -deltaG'o + RTln([ATP]/[ADP][Pi]) where deltaG'o is the standard free energy of ATP hydrolysis. Studies of the effects of deltaGp on NADH respiration and the reduction of NAD+ by succinate show that increasing values of deltaGp cause an inhibition of forward electron transfer and a stimulation of reverse electron transfer. Between deltaGp values of 7.6 and 13.0 kcal/mol the rate of NADH respiration decreased 3-fold and the rate of NAD+ reduction by succinate increased 3-fold. Indirect phosphorylation potential titration experiments as well as direct chemical measurements indicate that steady state levels of ATP, ADP, and Pi are established during NADH respiration which correspond to a deltaGp equal to 10.7 to 11.4 kcal/mol.