The Phosphoglycerate Kinase Reaction and its Metal Ion Specifity.

The present study shows that MgATP2- or MnATP2- as substrates of phosphoglycerate kinase can be replaced by CaATP2-, ZnATP2-, CoATP2- or NiATP2-. MnATP2- and NiATP2- are about 90% and 15%, respectively, and the other ATP4--metal ion complexes roughly 70% as good substrates as MgATP2-. No measurable activity was found with Be(II) or Fe(III). The effectiveness of the different substrate species appears to be determined by factors such as the size and polarizing capability of the metal ion as well as of the structure of the relevant metal ion complex and the rate of ligand dissociation processes. Detailed kinetics with Zn(II), Mn(II) and Co(II) showed that: (a) Zn2+ is a strong uncompetitive inhibitor of ZnATP2-, Ki approx. 0.02 mM. (b) Mn2+ is a competitive inhibitor of MnATP2- at concentrations ≥ 0.1 mM, Ki approx. 2.3 mM. This inhibition is dependent on the 3-P-glycerate concentration. At about 1 mM and higher concentrations Mn2+ acts as an uncompetitive inhibitor of mnATP2-. (c) Co2+ is a competitive inhibitor of CoATP2- at about 1 mM and higher concentrations, Ki approx. 3 mM. With CoATP2- as substrate the activity is slightly increased in the presence of free Co2+ and/or free ATP4- at concentrations < 0.5 mM. When the CoATP2- concentration is varied, the activity seems not to become constant at concentrations ten times the apparent Michaelis constant for CoATP2-. Equilibrium dialysis studies on the binding of Co2+ to the enzyme showed that this ion binds more strongly to the enzyme than, for example, Mn2+. This probably explains the differences in activation and inhibition observed with these two ions. The kinetic patterns obtained with the different metal ions indicate that Ni(II) behaves as Co(II), Cd(II) as Zn(II) and Ca(II) as Mg(II), which is somewhat similar in behaviour to Mn(II). [ABSTRACT FROM AUTHOR]