Evidence for a tyrosine residue at the active site of phosphoglucomutase and its interaction with vanadate.

Abstract

The rate of transfer of [32P]-labeled [rabbit skeletal muscle] phosphoglucomutase (.alpha.-D-glucose-1,6-bisphosphate:.alpha.-D-glucose-1-phosphate phosphotransferase, EC 2.7.5.1) to glucose increases dramatically between pH 8.5 and 10.5 with a half maximal rate at pH 9.8. This suggests the participation of a residue containing an ionizable group with a pK close to 10. The inhibition of enzyme activity obtained with tyrosine-derivatizing reactions.sbd.iodination, nitration, acetylation and diazo coupling.sbd.is strongly indicative of tyrosine participation. Thiol reagents, p-hydroxymercuribenzoate and ethyleneimine, were without effect. Vanadate and arsenate augmented the transfer reaction 200- and 2.5-fold, respectively, and lowered the pH optimum of the reaction.