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Tyrosine phosphorylation of phosphatase inhibitor 2
Author(s) -
Williams John P.,
Jo Hanjoong,
Hunnicutt Ruthann E.,
Brautigan David L.,
McDonald Jay M.
Publication year - 1995
Publication title -
journal of cellular biochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.028
H-Index - 165
eISSN - 1097-4644
pISSN - 0730-2312
DOI - 10.1002/jcb.240570307
Subject(s) - protein tyrosine phosphatase , phosphorylation , dephosphorylation , phosphatase , phosphopeptide , biochemistry , tyrosine , chemistry , microbiology and biotechnology , tyrosine phosphorylation , tyrosine kinase inhibitor , dusp6 , enzyme inhibitor , protein kinase inhibitor , protein kinase a , biology , enzyme , protein phosphatase 2 , genetics , cancer
Inhibitor 2 is a heat‐stable protein that complexes with the catalytic subunit of type‐1 protein phosphatase. The reversible phosphorylation of Thr 72 of the inhibitor in this complex has been shown to regulate phosphatase activity. Here we show that inhibitor 2 can also be phosphorylated on tyrosine residues. Inhibitor 2 was 32 P‐labeled by the insulin receptor kinase in vitro, in the presence of polylysine. Phosphorylation of inhibitor 2 was accompanied by decreased electrophoretic mobility. Dephosphorylation of inhibitor 2 by tyrosine phosphatase 1B, restored normal electrophoretic mobility. Phosphotyrosine in inhibitor 2 was detected by immunoblotting with antiphosphotyrosine antibodies and phosphoamino acid analysis. In addition, following tryptic digestion, one predominant phosphopeptide was recovered at the anode. The ability of inhibitor 2 to inhibit type‐1 phosphatase activity was diminished with increasing phosphorylation up to a stoichiometry of 1 mole phosphate incorporated/mole of inhibitor 2, where inhibitory activity was completely lost. These data demonstrate that inhibitor 2 can be phosphorylated on tyrosine residues by the insulin receptor kinase, resulting in a molecule with decreased ability to inhibit type‐1 phosphatase activity.