Phosphotyrosyl-protein phosphatase of TCRC-2 cells

Abstract

Homogenization of TCRC-2 cells yielded a phosphotyrosyl-protein phosphatase with a specific activity approximately 10-=fold higher in particulate than in soluble fractions. Over 90% of the phosphotyrosyl-protein phosphatase associated with the particles was solubilized with 1.0% Nonidet P-40. Chromatography of the detergent-solubilized particulate fraction on either wheat germ lectin-Sepharose or histone-Sepharose columns separated two major components of phosphatase activity. One peak (eluted with 200 mM NaCl from histone-Sepharose or with N-acetylglucosamine from the lectin column) contained both phosphotyrosyl-and phosphoseryl-protein phosphatase as well as p-nitrophenyl phosphatase activities. The other peak (eluted with 1.0 M NaCl from histone-Sepharose or not bound to the lectin column) contained essentially only phosphoseryl-protein phosphatase activity. Various agents (EDTA, p-nitrophenyl phosphate, fluoride) showed considerable differences in their ability to inhibit the two phosphatase fractions; of these, the most potent and selective inhibitor was orthovanadate. At micromolar concentrations, vanadate inhibited the fraction containing phosphotyrosyl-protein phosphatase and failed to inhibit the fraction containing only phosphoseryl-protein phosphatase activity. These data show that the particulate forms of phosphotyrosyl-protein phosphatase and p-nitrophenyl phosphatase represent the activities of very similar or identical proteins.