A model phosphatase 2C --> phosphatase 1 activation cascade via dual control of inhibitor-1 (INH-1) and DARPP-32 dephosphorylation by two inositol glycan putative insulin mediators from beef liver |
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Authors: | Huang L C Heimark D Linko J Nolan R Larner J |
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Affiliation: | Department of Pharmacology, University of Virginia School of Medicine, Charlottesville, Virginia 22908, USA. |
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Abstract: | Two inositol phosphoglycans (IPG) isolated from beef liver and designated as putative insulin mediators were demonstrated to reciprocally enhance the dephosphorylation of inhibitor-1 (INH-1) and DARPP-32, thus directly activating phosphatase 2C and disinhibiting phosphatase 1 in a potential protein phosphatase 2C --> phosphatase 1 cascade mechanism. One IPG termed pH 2.0, containing Dchiro-inositol and galactosamine, stimulated the dephosphorylation of INH-1 and DARPP-32 in a dose-dependent manner in the low micromolar range. A second, termed pH 1.3, containing myo-inositol glucosamine and mannose acted reciprocally to inhibit the cAMP-dependent protein kinase phosphorylation of INH-1 and DARPP-32 in a dose-dependent manner in the low micromolar range. These model experiments are discussed in terms of the observed dephosphorylation of INH-1 with insulin action documented in the literature and the activation of both phosphatase 1 and 2C described in intact cells and in vivo with insulin action. |
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