Product inhibition and 18O exchange experiments suggest that the Yersinia protein-tyrosine phosphatase-catalyzed phosphate monoester hydrolysis proceeds through at least two different chemical steps, i.e. the formation and breakdown of a covalent phosphoenzyme intermediate. The pH dependence of k(cat) values is bell-shaped, with the apparent pK(a) derived from the acidic limb of the profile at 4.6 for both p-nitrophenyl phosphate and β-naphthyl phosphate, whereas the apparent pK(a) derived from the basic limb of the profile is substrate-dependent, with apparent pK(a) values of 5.2 and 5.8 for p-nitrophenyl phosphate and β-naphthyl phosphate, respectively. Twelve aryl phosphates with leaving groups having pK(a) values from ~7 to 10 are also examined as substrates at two pH values. At pH 4.0, the β(Ig) value is effectively zero, whereas at pH 7.5, a β(1g) value of 0.16 is observed. Collectively, our results suggest that the rate-determining step under acidic conditions corresponds to the breakdown of the phosphoenzyme intermediate, whereas under more alkaline conditions, substrate effects also contribute to the rate-limiting step. A model is proposed for the mechanism of the Yersinia protein-tyrosine phosphatase-catalyzed reaction.
|Original language||English (US)|
|Number of pages||6|
|Journal||Journal of Biological Chemistry|
|State||Published - Mar 18 1994|
ASJC Scopus subject areas
- Molecular Biology
- Cell Biology