Regulation of alpha-glycerophosphate dehydrogenase activity in human term placental mitochondria.
1. alpha-Glycerophosphate dehydrogenase (sn-glycerol-3-phosphate:(acceptor) oxidoreductase, EC 1.1.99.5) activity in mitochondria isolated from human term placenta was found to be inhibited by ethyleneglycolbis (beta-aminoethyl ether)-N,N'-tetraacetic acid (EGTA). Addition of an excess of calcium ions to the incubation medium completely restored the original activity. The concentration of free calcium ion required to activate the alpha-glycerophosphate dehydrogenase was found to vary between 10 and 100 nM. 2. The pH optimum for alpha-glycerophosphate dehydrogenase activity varied with substrate concentration. The pH optima were 7.4 and 8.0 in the presence of 2 or 8 mM alpha-glycerophosphate, respectively. The apparent Km for alpha-glycerophosphate also varied with pH; the values being 0.4 mM at pH 7.05, 1.5 mM at pH 7.8, and 3.5 mM at pH 8.5. 3. alpha-Glycerophosphate dehydrogenase activity was inhibited by palmitoyl-CoA in a competitive manner with an apparent Ki value of about 10 muM. This inhibition was less pronounced in the presence of calcium or magnesium ions. 4. The activity of alpha-glycerophosphate dehydrogenase was inhibited by phosphoenolpyruvate, D- and DL-glyceraldehyde 3-phosphate and 3-phosphoglyceric acid, in a competitive manner, the apparent Ki values being 0.5, 0.95, 0.12 and 1.5 mM, respectively. 5. alpha-Glycerophosphate dehydrogenase activity in human placental mitochondria was found to be more sensitive to phosphoenolpyruvate, than the activity of the same enzyme in rat skeletal muscle mitochondria. alpha-Glycerophosphate dehydrogenase activity in rat brown adipose tissue mitochondria was only slightly affected by phosphenolpyruvate under the same conditions. 6. The data obtained suggest that the activity of alpha-glycerophosphate dehydrogenase in human placental mitochondria may be controlled by changes of the cytosolic level of palmitoyl-CoA, some glycolytic intermediates, and pH.
D002001:Adipose Tissue, Brown / Q000201:enzymology; D000818:Animals; D002118:Calcium / Q000494:pharmacology; D003065:Coenzyme A / Q000494:pharmacology; D004533:Egtazic Acid / Q000494:pharmacology; D004789:Enzyme Activation / Q000187:drug effects; D005260:Female; D005987:Glyceraldehyde-3-Phosphate Dehydrogenases / Q000378:metabolism*; D006801:Humans; D007700:Kinetics; D008928:Mitochondria / Q000201:enzymology*; D008931:Mitochondria, Muscle / Q000201:enzymology; D009928:Organ Specificity; D010169:Palmitic Acids / Q000494:pharmacology; D010920:Placenta / Q000201:enzymology*; D011247:Pregnancy; D051381:Rats
D010169:Palmitic Acids; D004533:Egtazic Acid; D005987:Glyceraldehyde-3-Phosphate Dehydrogenases; D003065:Coenzyme A; D002118:Calcium