Modulation of oxidative phosphorylation by Mg2+ in rat heart mitochondria.
The effect of varying the Mg2+ concentration on the 2-oxoglutarate dehydrogenase (2-OGDH) activity and the rate of oxidative phosphorylation of rat heart mitochondria was studied. The ionophore A23187 was used to modify the mitochondrial free Mg2+ concentration. Half-maximal stimulation (K0.5) of ATP synthesis by Mg2+ was obtained with 0.13 +/- 0.02 mM (n = 7) with succinate (+rotenone) and 0.48 +/- 0.13 mM (n = 6) with 2-oxoglutarate (2-OG) as substrates. Similar K0.5 values were found for NAD(P)H formation, generation of membrane potential, and state 4 respiration with 2-OG. In the presence of ADP, an increase in Pi concentration promoted a decrease in the K0.5 values of ATP synthesis, membrane potential formation and state 4 respiration for Mg2+ with 2-OG, but not with succinate. These results indicate that 2-OGDH is the main step of oxidative phosphorylation modulated by Mg2+ when 2-OG is the oxidizable substrate; with succinate, the ATP synthase is the Mg2+-sensitive step. Replacement of Pi by acetate, which promotes changes on intramitochondrial pH abolished Mg2+ activation of 2-OGDH. Thus, the modulation of the 2-OGDH activity by Mg2+ has an essential requirement for Pi (and ADP) in intact mitochondria which is not associated to variations in matrix pH.
Rodríguez-Zavala
J S
JS
Departamento de Bioquímica, Instituto Nacional de Cardiología, México, D.F. 14080, México.
Moreno-Sánchez
R
R
D000818:Animals; D000001:Calcimycin / Q000494:pharmacology*; D007476:Ionophores / Q000494:pharmacology*; D007655:Ketoglutarate Dehydrogenase Complex / Q000378:metabolism*; D008274:Magnesium / Q000378:metabolism*; D008297:Male; D008929:Mitochondria, Heart / Q000378:metabolism*; D010085:Oxidative Phosphorylation; D051381:Rats; D017208:Rats, Wistar
D007476:Ionophores; D000001:Calcimycin; D007655:Ketoglutarate Dehydrogenase Complex; D008274:Magnesium