Inhibition of phosphoglycerate kinase by products and product homologues.

Abstract

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 concentrations.The main catalytic reaction suits a pattern that is consistent with a rapid equilibrium random mechanism.