Partia1 Purification Pea Nuclei with and Characterization of an Enzyme from Protein Tyrosine Phosphatase Activity'

A pea (Pisum sativum 1.) nuclear enzyme with protein tyrosine phosphatase activity has been partially purified and characterized. The enzyme has a molecular m a s of 90 kD as judged by molecular sieve column chromatography and by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Like animal protein tyrosine phosphatases it can be inhibited by low concentrations of molybdate and vanadate. It i s also inhibited by heparin and spermine but not by either the acid phosphatase inhibitors citrate and tartrate or the protein serine/threonine phosphatase inhibitor okadaic acid. l h e enzyme does not require Ca2+, MgZ+, or Mn2+ for i ts activity but is stimulated by ethylenediaminetetraacetate and by ethyleneglycolbis(P-aminoethyl ether)-N,N'-tetraacetic acid. It dephosphorylates phosphotyrosine residues on the four different 32P-tyrosine-labeled peptides tested but not the phosphoserine/threonine residues on casein and histone. Like some animal protein tyrosine phosphatases, it has a variable pH optimum depending on the substrate used: the optimum is 5.5 when the substrate i s [32Pltyrosine-labeled lysozyme, but it is 7.0 when the substrate i s [32P]tyrosine-labeled poly(g1utamic acid, tyrosine). It has a K,,, of 4 p~ when the lysozyme protein is used as a substrate.