Effect of magnesium ion (Mg2+) and the magnesium adenosine triphosphate ion (MgATP2-) on pigeon liver pyruvate carboxylase.
Kinetic methods have been used to determine whether Mg2+ and MgATP2- play an important role in regulating pigeon liver pyruvate carboxylase [pyruvate: CO2 ligase (ADP), EC 6.4.1.1]. Mg2+ not only forms a complex with ATP4- (MgATP2-) but is also required for the enzyme activation (and probably for the binding of MgATP2- to this enzyme). Contrary to the results of other investigators, the MgATP2- complex was not found to activate pigeon liver pyruvate carboxylase. We could not demonstrate homotropic cooperativity with MgATP2-. Excess Mg2+ induced allosteric stimulation of the enzymatic activity at different concentrations of MgATP2-. With different Mg2+ concentrations, changes also occurred in the apparent Km, Vmax and Rs values. Without excess of Mg2+ (heterotropic effector) only about 2% of the total enzymic activity available could be demonstrated in the presence of MgATP2-. It is concluded that Mg2+ exhibits a homotropic cooperative effect and is required for the activation of this enzyme. Mg2+ may bind either to a specific effector site, at the active site, or at the binding site for MgATP2- which is capable of functioning as an effector site and in this way facilitates the carboxylation of pyruvate.
D000255:Adenosine Triphosphate / Q000494:pharmacology*; D000494:Allosteric Regulation; D000818:Animals; D001665:Binding Sites; D010856:Columbidae; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008099:Liver / Q000201:enzymology*; D008274:Magnesium / Q000494:pharmacology*; D011485:Protein Binding; D011766:Pyruvate Carboxylase / Q000378:metabolism*
D000255:Adenosine Triphosphate; D011766:Pyruvate Carboxylase; D008274:Magnesium