Characterization of a phosphotyrosyl protein phosphatase activity associated with a phosphoseryl protein phosphatase of Mr = 95,000 from bovine heart.
A cytosolic phosphoprotein phosphatase of Mr = 95,000 purified from bovine cardiac muscle, which contains a catalytic subunit of Mr = 35,000, is known to be associated with a Mg2+-activated p-nitrophenyl phosphatase activity. We have found that the enzyme preparation is also active toward phosphotyrosyl-IgG and -casein phosphorylated by pp60v-src, the transforming gene product of Rous sarcoma virus. The properties of this phosphotyrosyl protein phosphatase activity closely resemble those of the p-nitrophenyl phosphatase activity but sharply differ from those of the phosphorylase phosphatase activity. Comparative studies of the activities of the Mr = 95,000 phosphatase, bovine kidney alkaline phosphatase, and ATP X Mg-dependent phosphatase toward phosphoseryl, phosphothreonyl, and phosphotyrosyl proteins and p-nitrophenyl phosphate under various conditions have been carried out. The results indicate that the Mr = 95,000 enzyme exhibits higher activity toward phosphoseryl and phosphothreonyl proteins than toward phosphotyrosyl proteins, while the kidney alkaline phosphatase preferentially dephosphorylates phosphotyrosyl proteins. ATP X Mg-dependent phosphatase is inactive toward phosphotyrosyl proteins.
D000818:Animals; D002417:Cattle; D004355:Drug Stability; D004591:Electrophoresis, Polyacrylamide Gel; D006358:Hot Temperature; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008970:Molecular Weight; D009206:Myocardium / Q000201:enzymology*; D010749:Phosphoprotein Phosphatases / Q000302:isolation & purification* / Q000378:metabolism; D013379:Substrate Specificity
D010749:Phosphoprotein Phosphatases