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

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Abstract
Using [32P]P-Tyr-IgG and [32P]P-Tyr-casein phosphorylated by pp60v-scr 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: these 2 enzymatic activities co-purify to apparent homogeneity; they co-migrated on polyacrylamide gel electrophoresis, ion-exchange and gel filtration chromatographies; they exhibit identical thermostability; and 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. Prostatic acid phosphatase may function in vivo as a phosphotyrosyl-protein phosphatase.