Modulation of 2-oxoglutarate dehydrogenase and oxidative phosphorylation by Ca2+ in pancreas and adrenal cortex mitochondria.
The effect of external free Ca2+ ([Ca2+]ex) on the 2-oxoglutarate dehydrogenase (2-OGDH) activity and the rate of state 3 respiration was studied in dog pancreas and adrenal cortex mitochondria. A method for the preparation of mitochondria from pancreas, free of zymogen granules, was developed. The mitochondria showed high respiratory control values and maintained adequate ADP/O ratios in the course of several hours. Half-maximal stimulation (K0.5) of 2-OGDH activity and state 3 respiration by Ca2+ was decreased twofold by spermine, in both pancreas and adrenal cortex mitochondria incubated with Mg2+; Na+ increased the K0.5 value for Ca2+ in both kinds of mitochondria. The matrix Ca2+ content was enhanced by spermine at different [Ca2+]ex. The Ca2+ gradient ([Ca2+]m/[Ca2+]ex) determined in Fluo 3-loaded pancreas mitochondria was found to be below 1, either in the presence of Na+ or in the absence of spermine. The protonmotive force was increased by 1 microM Ca2+, in state 3 conditions, by 6-8 mV; lower Ca2+ concentrations kept the H+ gradient rather constant. An increase in the spermine/Mg2+ ratio at constant external Ca2+ resulted in stimulation of the 2-OGDH activity and state 3 respiration. The data indicate that matrix Ca2+ may regulate the rate of ATP synthesis in pancreas and adrenal cortex mitochondria, through the modulation of 2-OGDH and the maintenance of a high H+ gradient. In addition to changes in external Ca2+, the variation in the spermine/Mg2+ ratio may also exert control of oxidative phosphorylation.
Moreno-Sánchez
R
R
Departamento de Bioquímica, Instituto Nacional de Cardiología, México, D.F., México.
Rodríguez-Enríquez
S
S
Cuéllar
A
A
Corona
N
N
D000302:Adrenal Cortex / Q000378:metabolism*; D000818:Animals; D002118:Calcium / Q000378:metabolism* / Q000494:pharmacology; D004285:Dogs; D004789:Enzyme Activation; D017136:Ion Transport; D007655:Ketoglutarate Dehydrogenase Complex / Q000378:metabolism*; D008854:Microscopy, Electron; D008928:Mitochondria / Q000378:metabolism* / Q000648:ultrastructure; D010084:Oxidation-Reduction; D010179:Pancreas / Q000378:metabolism*; D010766:Phosphorylation; D013096:Spermine / Q000494:pharmacology
D013096:Spermine; D007655:Ketoglutarate Dehydrogenase Complex; D002118:Calcium