Percival M D, Doherty K, Gresser M J
Department of Chemistry, Simon Fraser University, Burnaby, British Columbia, Canada.
Biochemistry. 1990 Mar 20;29(11):2764-9. doi: 10.1021/bi00463a020.
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.
磷酸葡萄糖变位酶受到由α-D-葡萄糖1-磷酸（Glc-1-P）和无机钒酸盐（Vi）形成的复合物的抑制。稳态下的抑制作用以及达到稳态的速率均取决于Glc-1-P和Vi的浓度。该抑制作用相对于α-D-葡萄糖1,6-二磷酸（Glc-P2）具有竞争性，并且归因于Glc-1-P的6-钒酸酯（V-6-Glc-1-P）与磷酸葡萄糖变位酶的脱磷酸形式（E）的结合。通过稳态动力学测量确定，在pH 7.4时V-6-Glc-1-P的抑制常数为2×10⁻¹² M。达到稳态的一级速率常数随抑制剂浓度呈双曲线增加。结果与V-6-Glc-1-P与E的快速平衡结合一致，解离常数为1×10⁻⁹ M，随后是E·V-6-Glc-1-P复合物向另一种物质E*·V-6-Glc-1-P的限速转化，一级速率常数为4×10⁻² s⁻¹。确定的逆反应速率常数，即E*·V-6-Glc-1-P转化为E·V-6-Glc-1-P的速率常数为2.5×10⁻⁴ s⁻¹。E*·V-6-Glc-1-P的形成也可通过葡萄糖6-钒酸酯与磷酸葡萄糖变位酶的磷酸化形式（E-P）结合，随后进行磷酸基转移和酶-产物复合物的重排而发生。
