Inhibition of phosphoglucomutase by vanadate

Abstract

Phosphoglucomutase is inhibited by a complex formed from alpha-D-glucose 1-phosphate (Glc-1-P) and inorganic vanadate (Vi). Both the inhibition at steady state and the rate of approach to steady state are dependent on the concentrations of both Glc-1-P and Vi. Inhibition is competitive versus alpha-D-glucose 1,6-bisphosphate (Glc-P2) and is ascribed to binding of the 6-vanadate ester of Glc-1-P (V-6-Glc-1-P) to the dephospho form of phosphoglucomutase (E). The inhibition constant for V-6-Glc-1-P at pH 7.4 was determined from steady-state kinetic measurements to be 2 x 10(-12) M. The first-order rate constant for approach to steady state increases hyperbolically with inhibitor concentration. The results are consistent with rapid equilibrium binding of V-6-Glc-1-P to E, with dissociation constant 1 x 10(-9) M, followed by rate-limiting conversion of the E.V-6-Glc-1-P complex to another species, E*.V-6-Glc-1-P, with first-order rate constant 4 x 10(-2)s-1. The rate constant determined for the reverse reaction, conversion of E*.V-6-Glc-1-P to E.V-6-Glc-1-P, is 2.5 x 10(-4)s-1. Formation of E*.V-6-Glc-1-P can also occur via binding of glucose 6-vanadate to the phospho form of phosphoglucomutase (E-P) followed by phosphoryl transfer and rearrangement of the enzyme-product complex.

Influence of vanadium(V) complexes on the catalytic activity of ribonuclease A. The role of vanadate complexes as transition state analogues to reactions at phosphate

“…These two parameters correspond to -37 and -62 kllmol, respectively, for the association energy. Values close to this are also found for phosphoglucomutase where the K, for 1,6-bisphosphoglucose is equal to 4.8 x lo-' M while Ki for 6-vanadio-glucose-l-phosphate is 2 x lo-'" (13). These constants correspond to AG = -41 and -66 Wlmol, respectively.…”

“…Enzyme kinetics studies have also been carried out in conjunction with these NMR studies. The results obtained here have been compared with those reported for phosphoglycerate mutase (12) and for phosphoglucomutase (13,14).…”

The Chemistry and Biochemistry of Vanadium and the Biological Activities Exerted by Vanadium Compounds

“…The inhibition constant for 1-phosphoglucose-6-vanadate at pH 7.4 was determined from steady-state kinetic measurements to be 2 × 10 -12 M. 393 Calculations of the binding energy of the vanadate complex in phosphoglucomutase revealed an excess of binding energy, over the analogous phosphate derivative, of about 25 kJ/mol and represents about 40% of that expected to be available for a trigonal-bipyramidal transition state. 49 The effects of vanadate on phosphoglycerate mutase have also been studied.…”

Vanadium and proteins: Uptake, transport, structure, activity and function

“…The inhibition was attributed to the formation of 1-phosphoglucose-6-vanadate(V) and 1-vanadofructose-6-phosphate, which forms a stable complex with the protein [5]. An inhibition constant of 210 −12 M was determined for 1-phosphoglucose-6-vanadate(V) at pH 7.4 [312].…”