The Effect of Phenol-Based Ligands on Vanadate Inhibition of the Protein Tyrosine Phosphatase Yop51*D162.

Abstract

Studies of vanadate inhibition of the protein tyrosine phosphatase (PTP) YOP*[delta]162 were undertaken. Vanadate was found to be reversible competitive inhibitor with Ki,c = 1.64 +/- 0.07 [mu]M at pH = 5.5 and Ki,c = 3.05 +/- 0.05 [mu]M at pH = 7.3. Vanadate was not an uncompetitive inhibitor at either pH.A variety of ligands were surveyed to determine if they could enhance vanadate inhibition of PTP. Two, 4-nitrocatechol and 2-amino-4-nitrophenol, formed equilibrium complexes with vanadate that irreversibly inactivated PTP. The ligands catechol, protocatechol, and 3,4-dihydroxyphenylalanine (l-DOPA) reacted with vanadate to produce an inactivator of PTP. The inactivation rate had an exponential dependence on time-squared. Further studies of the vanadate/l-DOPA system demonstrate that the vanadate and l-DOPA react slowly to form a complex that inhibits PTP rapidly and stoichiometrically inhibits PTP. This inhibition is also selective for PTP, in that, it has no effect on the serine/threonine phosphatases acid or alkaline phosphatases. Spectroscopic data suggests the identity of the inhibitor is [VIVO(l-DOPA)2]2-.It was also determined that o-benzoquinone and tetrachloro-o-benzoquinone could inactivate PTP, while p-quinones had no effect on the activity of PTP.