Effect of thyroidectomy on oxidative phosphorylation mechanisms in rat liver mitochondria.
(1) In the presence of succinate, 2,4-dinitrophenol raised the oxygen consumption rate of state 3 liver mitochondria, whatever the thyroid state. The rise was clearly greater in thyroidectomized than in normal rats, but the uncoupled state 3 mitochondria of thyroidectomized rats nevertheless consumed oxygen more slowly than normal rat mitochondria. Thyroidectomy therefore weakened respiratory chain activity and phosphorylation reactions. (2) With beta-hydroxybutyrate as substrate, oxygen consumption V of state 3 mitochondria was greatly diminished in thyroidectomized rats, but the KM remained unchanged. In the presence of succinate, state 3 respiration was not affected by thyroidectomy when substrate concentrations were low, but diminished at concentrations above 3 mM. (3) Respiratory chain activity was estimated by determining the succinate cytochrome c reductase activity. After thyroidectomy, catalytic efficiency (V/KM) dropped by 60% in intact mitochondria at high concentrations of the substrate, but only by 30% when concentrations were low. In submitochondrial particles, thyroidectomy reduced V without changing KM. These results suggest that in thyroidectomized rats, succinate penetration is faster when substrate concentrations are low. (4) Mg2+ -stimulated ATPase activity dropped by 20% in thyroidectomized rats. In the presence of increasing concentrations of oligomycin, inhibition of ATPase activity was greater in normal than in thyroidectomized rat mitochondria. Thyroidectomy reduced by over 30% the ATPase activity actually involved in oxidative phosphorylation.
D019297:2,4-Dinitrophenol; D000251:Adenosine Triphosphatases / Q000378:metabolism; D000818:Animals; D017301:Ca(2+) Mg(2+)-ATPase; D004140:Dinitrophenols / Q000494:pharmacology; D007700:Kinetics; D008297:Male; D008930:Mitochondria, Liver / Q000378:metabolism*; D009840:Oligomycins / Q000494:pharmacology; D010085:Oxidative Phosphorylation / Q000187:drug effects; D010101:Oxygen Consumption / Q000187:drug effects; D010710:Phosphates / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains; D013384:Succinate Cytochrome c Oxidoreductase / Q000378:metabolism; D013965:Thyroidectomy
D004140:Dinitrophenols; D009840:Oligomycins; D010710:Phosphates; D013384:Succinate Cytochrome c Oxidoreductase; D000251:Adenosine Triphosphatases; D017301:Ca(2+) Mg(2+)-ATPase; D019297:2,4-Dinitrophenol