title: Effects of calcium ions on pyruvate kinase from human erythrocytes.
abstract: Ca2+ ions have a biphasic effect on the allosteric pyruvate kinase (EC 2.7.1.40) from human erythrocytes: Ca2+ is an activator at low phosphoenolpyruvate (PEP) concentrations: at increased PEP concentrations Ca2+ behaves as an inhibitor. In the presence of ATP the same effect was observed and at low PEP concentrations Ca2+ ions can completely abolish the ATP inhibitory effect. At high Ca2+ concentrations there is a loss of the cooperativity towards PEP. The enzyme activated by fructose-1,6-diphosphate (FDP) is inhibited by Ca2+ ions at all concentrations of PEP tested. Mg2+ ions are not able to counteract the activation by Ca2+ ions at low PEP concentrations. The results are interpreted on the basis of the model of Monod.
mesh_terms: D000255:Adenosine Triphosphate / Q000494:pharmacology; D000494:Allosteric Regulation; D002118:Calcium / Q000494:pharmacology*; D004789:Enzyme Activation / Q000187:drug effects; D004912:Erythrocytes / Q000187:drug effects / Q000201:enzymology*; D005636:Fructosephosphates / Q000494:pharmacology; D006801:Humans; D007700:Kinetics; D008274:Magnesium / Q000494:pharmacology; D010728:Phosphoenolpyruvate / Q000494:pharmacology; D011770:Pyruvate Kinase / Q000097:blood*
chemical_list: D005636:Fructosephosphates; D010728:Phosphoenolpyruvate; D000255:Adenosine Triphosphate; D011770:Pyruvate Kinase; D008274:Magnesium; D002118:Calcium