Characterization of phosphotyrosyl-protein phosphatase activity associated with calcineurin |
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Authors: | J Chernoff M A Sells H C Li |
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Institution: | Department of Biochemistry Mount Sinai School of Medicine of the City University of New York New York, New York 10029 USA |
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Abstract: | Calcineurin purified from bovine brain is shown to possess phosphotyrosyl -protein phosphatase activity towards proteins phosphorylated by the epidermal growth factor receptor/kinase. The phosphatase activity is augmented by Ca2+/calmodulin or divalent cation (Ni2+ greater than Mn2+ greater than Mg2+ greater than Co2+). In the simultaneous presence of all three effectors, the enzymatic activity is synergistically increased. Ca2+/calmodulin activates the Mg2+-supported activity by decreasing the Km value for phosphotyrosyl -casein from 2.2 to 0.6 microM, and increasing the Vmax from 0.4 to 4.6 nmol/min/mg. These results represent the first demonstration that calcineurin can dephosphorylate phosphotyrosyl -proteins and suggest a novel mechanism of activation of this enzyme. |
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Keywords: | To whom correspondence should be addressed |
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