Protein phosphotyrosine phosphatase purified from the particulate fraction of human placenta dephosphorylates insulin and growth-factor receptors.
Protein phosphatase activity specific for Tyr(P) (phosphotyrosine) residues (PTP-phosphatase) was found in the cytosol and particulate fractions of human placenta. In the particulate fraction, half of the PTP-phosphatase activity could be extracted with 1% Triton X-100. The PTP-phosphatase remaining in the Triton-insoluble residue was solubilized with 0.6 M-KCl plus 1% CHAPS (3-[(3-cholamidopropyl)-dimethylammonio]propane-1-sulphonate) and was purified 1850-fold by adsorption to DEAE-Sepharose, affinity chromatography on Zn2+-iminodiacetate-agarose, phosphocellulose adsorption, Fractogel filtration and Mono Q chromatography. The cytoskeleton-associated PTP-phosphatase was distinguished from acid, alkaline and other protein Ser(P) (phosphoserine)/Thr(P) (phosphothreonine) phosphatases by its neutral pH optimum, activity in the presence of EDTA, inhibition by Zn2+, vanadate, or molybdate, and low activity with either [Ser(P)]phosphorylase a or p-nitrophenyl phosphate. The PTP-phosphate displayed a Km of 0.15 microM with [Tyr(P)]serum albumin as substrate, 10-100-fold lower than the Km for previously described protein phosphatases. The cytoskeleton-associated PTP-phosphatase catalysed the dephosphorylation of receptors for insulin, insulin-like growth factor-1 and epidermal growth factor labelled by autophosphorylation. The properties of this PTP-phosphatase suggest that it plays a role in the regulation of hormone receptors and cytoskeleton proteins by reversible phosphorylation on tyrosine residues.
Roome
J
J
Section of Biochemistry, Brown University, Providence, RI 02912.
O'Hare
T
T
Pilch
P F
PF
Brautigan
D L
DL
D002458:Cell Fractionation; D003599:Cytoskeleton / Q000201:enzymology; D066246:ErbB Receptors / Q000378:metabolism; D006801:Humans; D017830:Octoxynol; D010749:Phosphoprotein Phosphatases / Q000302:isolation & purification* / Q000378:metabolism; D010766:Phosphorylation; D010920:Placenta / Q000201:enzymology*; D011092:Polyethylene Glycols; D017027:Protein Tyrosine Phosphatases; D011972:Receptor, Insulin / Q000378:metabolism
D011092:Polyethylene Glycols; D017830:Octoxynol; D066246:ErbB Receptors; D011972:Receptor, Insulin; D010749:Phosphoprotein Phosphatases; D017027:Protein Tyrosine Phosphatases