Thyroid-hormone control of state-3 respiration in isolated rat liver mitochondria.

Oxidative phosphorylation can be treated as two groups of reactions; those that generate protonmotive force (dicarboxylate carrier, succinate dehydrogenase and the respiratory chain) and those that consume protonmotive force (adenine nucleotide and phosphate carriers. ATP synthase and proton leak). Mitochondria from hypothyroid rats have lower rates of respiration in the presence of ADP (state 3) than euthyroid controls. We show that the kinetics of the protonmotive-force generators are unchanged in mitochondria from hypothyroid animals, but the kinetics of the protonmotive-force consumers are altered, supporting proposals that the important effects of thyroid hormone on state 3 are on the ATP synthase or the adenine nucleotide translocator.