Proton and vanadium-51 NMR studies of the interaction of vanadate and 2-vanadio-3-phosphoglycerate with phosphoglycerate mutase

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Abstract
The formation of complexes of vanadate with 2-phosphoglycerate and 3-phosphoglycerate have been studied using 51V nuclear magnetic resonance spectroscopy. Signals attributed to two 2,3-diphosphoglycerate analogues, 2-vanadio-3-phosphoglycerate and 2-phospho-3-vanadioglycerate, were detected but were not fully resolved from signals of inorganic vanadate and the anhydride formed between vanadate and the phosphate ester moieties of the individual phosphoglycerates. Equilibrium constants for formation of the two 2,3-bisphosphate analogues were estimated as 2.5 M-1 for 2-vanadio-3-phosphoglycerate and 0.2 M-1 for 2-phospho-3-vanadioglycerate. The results of the binding study are fully consistent with non-cooperativity in the binding of vanadiophosphoglycerate to the two active sites of phosphoglycerate mutase (PGM). 2-Vanadio-3-phosphoglycerate was found to bind to the dephospho form of phosphoglycerate mutase with a dissociation constant of about 1 x 10(-11) M at pH 7 and 7 x 10(-11) M at pH 8. Three signals attributed to histidine residues were observed in the 1H NMR spectrum of phosphoglycerate mutase. Two of these signals and also an additional signal, tentatively attributed to a tryptophan, underwent a chemical shift change when the vanadiophosphoglycerate complex was bound to the enzyme. The results obtained here are in accord with these vanadate-phosphoglycerate complexes being much more potent inhibitors of phosphoglycerate mutase than either monomeric or dimeric vanadate. The dissociation constant of 10(-11) M for 2-vanadio-3-phosphoglycerate is about 4 orders of magnitude smaller than the Km for PGM, a result in accordance with the vanadiophosphoglycerates being transition state analogues for the phosphorylation of PGM by 2,3-diphosphoglycerate.(ABSTRACT TRUNCATED AT 250 WORDS)

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