Modulation of 2-oxoglutarate dehydrogenase complex by inorganic phosphate, Mg(2+), and other effectors.
The interplay of inorganic phosphate (Pi) with other ligands such as Mg(2+), ADP, ATP, and Ca(2+) on the activation of 2-oxoglutarate dehydrogenase complex (2-OGDH) in both isolated enzyme complex and mitochondrial extracts was examined. Pi alone activated the enzyme, following biphasic kinetics with high (K(0.5) = 1.96+/-0.42 mM) and low (K(0.5) = 9.8+/-0.4 mM) affinity components for Pi. The activation by Pi was highly pH-dependent; it increased when the pH raised from 7.1 to 7.6, but it was negligible at pH values below 7.1. Mg-Pi and Mg-ADP, but not Mg-ATP, were more potent activators of 2-OGDH than free Pi and free ADP. ATP inhibited the 2-OGDH activity by chelating the free Mg(2+) and also as a Mg-ATP complex. With or without Mg(2+), ADP, and Pi activated the 2-OGDH by increasing the affinity for 2-OG and the V(m) of the reaction; ATP diminished the V(m), but it increased the affinity for 2-OG in the mitochondrial extract. Pi did not modify the 2-OGDH activation by Ca(2+). The results above mentioned were similar for both preparations, except for hyperbolic kinetics in the isolated enzyme and sigmoidal kinetics in the mitochondrial extracts when 2-oxoglutarate was varied. The data of this study indicated that physiological concentrations of Pi may exert a significant activation of 2-OGDH, which was potentiated by Mg(2+) and high pH, but surpassed by ADP.
Rodríguez-Zavala
J S
JS
Departamento de Bioquímica, Instituto Nacional de Cardiología, México, D.F., 14080, México.
Pardo
J P
JP
Moreno-Sánchez
R
R
D000244:Adenosine Diphosphate / Q000494:pharmacology; D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000494:pharmacology; D004789:Enzyme Activation; D006863:Hydrogen-Ion Concentration; D007655:Ketoglutarate Dehydrogenase Complex / Q000378:metabolism*; D007700:Kinetics; D008274:Magnesium / Q000378:metabolism*; D008929:Mitochondria, Heart / Q000187:drug effects / Q000201:enzymology*; D009243:NAD / Q000378:metabolism; D010710:Phosphates / Q000494:pharmacology*; D013552:Swine
D010710:Phosphates; D009243:NAD; D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate; D007655:Ketoglutarate Dehydrogenase Complex; D008274:Magnesium; D002118:Calcium