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PLANT PHYSIOLOGY , Vol 107, Issue 1 167-175, Copyright © 1995 by American Society of Plant Biologists

BIOCHEMISTRY AND ENZYMOLOGY

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

Y. L. Guo and S. J. Roux
Department of Botany, The University of Texas at Austin, Austin, Texas 78713

A pea (Pisum sativum L.) nuclear enzyme with protein tyrosine phosphatase activity has been partially purified and characterized. The enzyme has a molecular mass 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 is 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. The enzyme does not require Ca2+, Mg2+, or Mn2+ for its activity but is stimulated by ethylenediaminetetraacetate and by ethyleneglycolbis([beta]-aminoethyl ether)-N,N[prime]-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 is [32P]tyrosine-labeled lysozyme, but it is 7.0 when the substrate is [32P]tyrosine-labeled poly(glutamic acid, tyrosine). It has a Km of 4 [mu]M when the lysozyme protein is used as a substrate.


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Q. Xu, H.-H. Fu, R. Gupta, and S. Luan
Molecular Characterization of a Tyrosine-Specific Protein Phosphatase Encoded by a Stress-Responsive Gene in Arabidopsis
PLANT CELL, May 1, 1998; 10(5): 849 - 858.
[Abstract] [Full Text] [PDF]


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Copyright © 1995 by the American Society of Plant Biologists