title: Ca2+-mediated activation of phosphoenolpyruvate carboxykinase occurs via release of Fe2+ from rat liver mitochondria.
abstract: The addition of calcium chloride to rat liver homogenates resulted in activation of phosphoenolpyruvate carboxykinase by as much as 50%. The enhanced activity was inhibited by quinolinic acid; it was not additive with activation by FeCl2, and stimulation was prevented by 1,10-phenanthroline. Activation by calcium was lost when the particulate fractions of liver were removed, but an activating system could be reconstituted with isolated mitochondria, purified P-enolpyruvate carboxykinase, and purified ferroactivator. Iron-loaded mitochondria were more responsive to calcium than controls. A release of Fe2+ from washed mitochondria could be detected spectrophotometrically when 25-75 nmol of Ca/mg of protein were added to the mitochondrial suspension. If Ca2+ was buffered with ethylene glycol bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid, the threshold of Ca2+ necessary for release of Fe2+ was approximately 10(-7) M, with peak response between 5 X 10(-7) and 10(-6) M. Total Fe2+ detected was normally 20-30 pmol of Fe2+/mg of protein. The synthetic activator of P-enolpyruvate carboxykinase, 3-aminopicolinic acid, as well as other picolinic acid derivatives, is capable of withdrawing Fe2+ associated with the mitochondrial fraction; after incubation with mitochondria, 3-aminopicolinate will activate phosphoenolpyruvate carboxykinase in the absence of exogenous metal.
mesh_terms: D000818:Animals; D002118:Calcium / Q000494:pharmacology*; D003600:Cytosol / Q000378:metabolism; D004533:Egtazic Acid / Q000494:pharmacology; D004789:Enzyme Activation; D007501:Iron / Q000378:metabolism*; D007700:Kinetics; D008099:Liver / Q000378:metabolism; D008274:Magnesium / Q000494:pharmacology; D008930:Mitochondria, Liver / Q000201:enzymology*; D010729:Phosphoenolpyruvate Carboxykinase (GTP) / Q000378:metabolism*; D051381:Rats; D012430:Ruthenium Red / Q000494:pharmacology
chemical_list: D012430:Ruthenium Red; D004533:Egtazic Acid; D007501:Iron; D010729:Phosphoenolpyruvate Carboxykinase (GTP); D008274:Magnesium; D002118:Calcium