Kinetic characterization of bovine lung low-molecular-weight protein tyrosine phosphatase

Protein tyrosine phosphatase is an important class of enzymes that plays an essential role in the cellular proliferation, differentiation, and oncogenesis. In this paper we report characterization of a low-molecular-weight protein tyrosine phosphatase purified from bovine lung. The enzyme activity was essentially independent of metal ions and sensitive to sulfhydryl reagents. Both vanadate and inorganic phosphate are competitive inhibitors, with Ki values of 0.38 microM and 0.28 mM, respectively. Besides p-nitrophenyl phosphate, the enzyme was also able to efficiently hydrolyze tyrosine phosphate, beta-naphthyl phosphate, and flavine mononucleotide.