An analysis of phosphotyrosyl-protein phosphatases present in soluble protein extracts prepared from chicken embryo bodies

Abstract

<p>A phosphotyrosyl-protein phosphatase, designated pTPIII, was purified to near homogeneity from soluble extracts prepared from 11-day old chicken embryo bodies. SDS-PAGE analysis suggested that this pTP activity correlated with the presence of a 58 kd protein band in affinity purified enzyme preparations. The purified protein exhibited biochemical characteristics in common with a phosphotyrosyl-protein phosphatase purified from human placental protein extracts, pTP1B (Tonks et al., 1988a; Pallen et al., 1991), and thus may represent the chicken homolog of this protein. Two partial cDNA clones encoding phosphotyrosyl-protein phosphatases were also isolated. Both code for members of the transmembrane class of tyrosine specific protein phosphatases, and thus probably bear no relation to the pTPIII and pTPI activities purified from soluble protein extracts. One cDNA appeared to encode the COOH-terminus of the chicken homolog of LAR, while the second seemed to code for the chicken homolog of PTP-zeta. Two cDNAs encoding PTP-zeta were isolated, however the evidence presented suggested that both clones were likely derived from incompletely processed nuclear RNAs.</p>