The effect of phenol-based ligands on vanadate inhibition of the protein tyrosine phosphatase Yop51*D162

by 1966- Boyajian, Yvette Darlene

BOYAJIAN, YVETTE DARLENE. The Effect of Phenol-Based Ligands on Vanadate Inhibition of the Protein Tyrosine Phosphatase YOP51*?162. (Under the direction of Charles R. Cornman and Dennis W. Wertz.) Studies of vanadate inhibition of the protein tyrosine phosphatase (PTP) YOP*?162 were undertaken. Vanadate was found to be reversible competitive inhibitor with K = 1.64 ± 0.07 µM at pH = 5.5 and K = 3.05 ± 0.05 µM at pH = 7.3. Vanadate i,c i,c 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. ii