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Stoichiometric dissociation constants of complexes between the fully deprotonated 3-phosphoD-glyceric acid and Mg2+, Mn2+, Ca2+ Co2+, Zn2+, and Ni2+, respectively, were determined in 0.25 M NaCl at 25 °C. Potentiometric titrations of the ligand with these divalent, metal ions were performed over a pH range close to the pK for the final deprotonation step of the ligand. The observed pH changes were utilized to estimate the dissociation constants; both algebraic and graphical techniques were employed in the estimations. Under the experimental conditions 1:1 complexes were the predominant products. [ABSTRACT FROM AUTHOR]

This paper gives a presentation of ADP and AMP inhibition of phosphoglycerate kinase with MgATP2- and 3-phospho-D-glycerate as substrates at high and low Mg2+ concentrations and pH 7.8. The enzyme seems to contain at least two nucleotide binding sites, one presumably binding to MgATP2- and the other to ADP3-. The ADP3- binding site might bind MgADP1- also. AMP2- competes for the same form of the enzyme, probably the same site, as MgATP2-. ADP3- and MgADP1- are competive inhibitors and AMP2- is a non-competitive inhibitor of 3-P-glycerate. Values of the inhibition constant, Ki, for ADP3- at low Mg2+ level and MgADP1- at high Mg2+ level are 0.2 and 0.02 mM, respectively. The latter value is about ten times less than the expected Michaelis constant for corresponding substrate in the reverse reaction. Ki for AMP is about 2.0 mM at both low and high Mg2+ concentrations but the inhibition is stronger at a high than at a low Mg2+ level, probably caused by conformational and/or other -differences of the enzyme at these two metal ion concentration. The main catalytic reaction suits a pattern that is consistent with a rapid equilibrium random mechanism. [ABSTRACT FROM AUTHOR]

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]