Factors affecting the rate and energetics of mitochondrial oxidative phosphorylation.

Mitochondrial oxidative phosphorylation in vivo is dependent on the degree of reduction of the intramitochondrial reducing power ([NADH]/[NAD+], cytoplasmic energy state ([ATP]/[ADP][Pi]) and intracellular oxygen pressure. Each parameter is independently regulated, and increased reducing power by activating the mitochondrial dehydrogenases allows higher energy state at a given rate of ATP synthesis or a higher rate of ATP synthesis at a given energy state. The mitochondrial respiratory rate is determined by demand, i.e., the rate of ATP utilization by the cell, while the cellular energy state at that demand level is determined by supply, i.e., activity of the dehydrogenases expressed as [NADH]/[NAD+] and of cytoplasmic oxygen pressure.