Influence of inorganic pyrophosphate on the kinetics of muscle pyruvate kinase: a simple nonallosteric feedback model.
Potassium pyrophosphate was used instead of ATP as a model ligand for magnesium cation for the study of effector influence on the kinetics of pyruvate kinase muscle isozyme M(1). The pyruvate kinase activation by low concentration of pyrophosphate and inhibition by high concentration of pyrophosphate was considered to be the result of reversible reactions of magnesium cation with pyrophosphate, ADP, ATP, and PEP. The apparent K(m) and V(m) or in some cases the pseudo-first order reaction rate constant (instead of K(m) and V(m)) of pyruvate kinase at any given pyrophosphate concentration were analysed as a function of concentration of free magnesium cation and its complexes with all ligands present in an assay mixture. The functions of reaction parameters with respect to concentration of magnesium complexes indicate the coexistence in the reaction mixture of simple and mixed complexes of magnesium cation with substrates, pyrophosphate, and an enzyme-substrate complex. The parameters of the simulated reaction for the proposed interactions fit the measured experimental data. A simple model with nonallosteric feedback has been proposed. According to this model, mutual and simultaneous interactions of reaction products with substrates and with an enzyme result in the coexistence of simple and mixed, labile and inert complexes.
Department of Experimental and Applied Biology, University of Opole, Kominka 4, Poland. kuczek@uni.opole.pl
Marian
M
Kuczek
D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D002417:Cattle; D011756:Diphosphates / Q000378:metabolism*; D005246:Feedback; D066298:In Vitro Techniques; D007527:Isoenzymes / Q000378:metabolism; D007700:Kinetics; D007770:L-Lactate Dehydrogenase / Q000378:metabolism; D008274:Magnesium / Q000378:metabolism; D008954:Models, Biological; D009132:Muscles / Q000201:enzymology*; D010728:Phosphoenolpyruvate / Q000378:metabolism; D011770:Pyruvate Kinase / Q000378:metabolism*
D011756:Diphosphates; D007527:Isoenzymes; D010728:Phosphoenolpyruvate; D000255:Adenosine Triphosphate; D007770:L-Lactate Dehydrogenase; D011770:Pyruvate Kinase; D008274:Magnesium