Insulin treatment of isolated liver plasma membranes induced the release of 5′-nucleotidase and alkaline phosphatase. This effect was maximal at physiological hormone concentrations, being 36% and 17% for 5′-nucleotidase and alkaline phosphatase respectively, and was fully mimicked by the phosphatidylinositol specific phospholipase C (PI-PLC), thus confirming the presence of a glycosyl-phosphatidylinositol anchoring-system for these exofacial enzymatic proteins. The complete inhibition of insulin dependent enzyme release by neomycin is strongly supportive of an involvement of membrane-located PI-PLC activity. In addition, the insulin-like effect on enzyme release induced by the GTP non-hydrolysable analog, GTP-γ-S, and its sensitivity to the pertussis toxin are in favour of a mediatory role exerted by the G proteins system, in the transduction of some actions of insulin.

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