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  • Title: The calcium dependence of insulin degradation by rat skeletal muscle.
    Author: Ryan MP, Gifford JD, Solomon SS, Duckworth WC.
    Journal: Endocrinology; 1985 Oct; 117(4):1693-8. PubMed ID: 3928338.
    Abstract:
    The effect of calcium on insulin degradation by intact or homogenized skeletal muscle, by skeletal muscle cytosol, and by partially purified skeletal muscle insulin-degrading protease activity was examined. After a 15-min lag phase, intact soleus muscles degraded [125I]insulin to trichloroacetic acid-soluble products in a time-dependent fashion. Degradation was accelerated by the addition of calcium (greater than or equal to 1 mM), such that maximal stimulation (2-fold) was obtained with 10 or 25 mM calcium. Calcium stimulated insulin degradation by skeletal muscle homogenate and by cytosol in a nearly identical manner. Furthermore, after inactivation of the purified skeletal muscle, insulin-degrading protease by dialysis against EDTA, this enzyme was reactivated fully (greater than 80%) by a 100 microM concentration of free Ca2+. These observations identify a previously unrecognized but important influence of calcium on cellular insulin handling and provide further evidence for a major role of the calcium-activated enzyme, insulin protease, in cellular insulin degradation.
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