A phosphotyrosyl‐protein phosphatase activity associated with acid phosphatase from human prostate gland

Using [³²P]P‐Tyr‐IgG and [³²P]P‐Tyr‐casein phosphorylated by pp60^v‐src as substrates, studies on the phosphotyrosyl‐protein phosphatase activity in human prostate gland indicate that it is associated with prostatic acid phosphatase. Evidence to support this conclusion include the following: (a) these two enzymatic activities co‐purify to apparent homogeneity; (b) they co‐migrated on polyacrylamide gel electrophoresis, ion‐exchange and gel filtration chromatographies; (c) the exhibit identical thermostability; and (d) the phosphotyrosyl‐protein phosphatase activity is sensitive to inhibition by p‐nitrophenyl phosphate and by several classical inhibitors of prostatic acid phosphatase including l(+)‐tartrate, molybdate, vanadate and NaF. The purified enzyme exhibits high specificity towards phosphotyrosyl‐proteins with little activity towards several phosphoseryl‐proteins and phosphothreonyl‐proteins examined. The present findings indicate that prostatic acid phosphatase may function in vivo as a phosphotyrosyl‐protein phosphatase.