Protein tyrosine phosphatases (PTPs) play a central role in cellular signaling processes, resulting in an increased interest in modulating the activities of PTPs. We therefore decided to undertake a detailed enzyme kinetic evaluation of various transmembrane and cytosolic PTPs (PTPalpha, PTPbeta, PTPis an element of, CD45, LAR, PTP1B and SHP-1), using pNPP as substrate. Most noticeable is the increase in the turnover number for PTPbeta with increasing pH and the weak pH-dependence of the turnover number of CD45. The kinetic data for PTPalpha-D1 and PTPalpha-D1D2 suggest that D2 affects the catalysis of pNPP. PTPis an element of and the closely homologous PTPalpha behave differently. The K-m data were lower for PTPis an element of than those for PTPalpha, while the inverse was observed for the catalytic efficiencies.
- p-Nitrophenyl phosphate
- Protein tyrosine phosphatase catalysis
- Substrate recognition