Phospholipase insulin

Other proteins show much bigger changes [e.g. the tyrosine of carb-oxypeptidase1 and the ends of the insulin chains (Hodgkin2)]. Still others seem to show gross changes [e.g., phospholipases (our own unpublished work)]. Finally, there are proteins that are almost random—chromogranin A and phosphovitin.3... 

It was shown, however, that the ability of insulin to release GIPs could be mimicked by an inositol phospholipid-specific phospholipase C. This enzyme is distinct from the phospholipidase C which acts to break down polyphosphatidylinositols as it acts specifically on phosphatidylinositol and has been used to release proteins which are anchored to membranes by the covalent attachment to phosphatidylinositol... 

If insulin does act to stimulate such a specific phospholipase then one might well expect diacylglycerol (DAG) to be produced. Indeed, this has been shown to be the... 

There is now considerable evidence to suggest that hormones which stimulate inositol phospholipid metabolism do so through a distinct G-protein [90-92]. It is thus possible that insulin might activate a G-protein in order to stimulate the proposed phosphatidylinositol-specific phospholipase C claimed to produce the GIPs insulin mediator (Fig. 4). 

Modulation of Insulin Secretion via Adenylate Cyclase and Phospholipase C (PLC). 92... 

Secretion of insulin results from the action of initiators and modulators on the secretory mechanism. Whereas initiators cause the discharge of insulin by depolarization of the B-cell and subsequent influx of Ca +, modulation (i.e. amplification and/or attenuation) is mediated mainly by activating and/or inactivating the adenylate cyclase and/or phospholipase C systems. 

In Xenopus o(x es (126,134), treatment with metformin has been shown to increase insulin receptor tyrosine kinase activity associated with activation of phospholipase C and increased levels of IPg and intracellular Ca. Thus metformin, through increasing receptor tyrosine kinase activity, may facilitate IRS protein phosphorylation and activation of phosphatidylinositol-3-kinase, leading to increased glucose uptake. 

Muller, G., Grey, S., Jung, C., and Bandlow, W. Insulin-like signaling in yeast modulation of protein phosphatase 2A, protein kinase A, cAMP-specific phosphodiesterase, and glycosyl-phospha-tidylinositol-specific phospholipase C activities. Biochemistry, 2000, 39, 1475-1488. 

M. Rodbell and A. B. Jones, Metabolism of isolated fat cells. 3. Tlie similar inhibitory action of phospholipase C and insulin on lipolysis stimulated by lipolytic hormones and theophylline, J. Biol. Chem., 1966, 241, 140-142. 

G. Muller, W. Frick, A. Crecelius,and S. Wied, Tlie insulin- and sulphonylurea-in-ducible glycosylphosphatidylinositol-spe-cific phospholipase C controles the localization and activity of signahng proteins in hpid rafts of adipocytes. Signal Transduction, Mediator, Genes, 2003, 4, p. 175. 

G. Muller, E.A. Dearey, A. Korndor-EER, and W. Bandlow, Stimulation of a glycosyl-phosphatidylinositol-specific phospholipase by insulin and the sulfonylurea, glimepiride, in rat adipocytes depends on increased glucose transport, J. Cell. Biol., 1994, 126, 1267-1276. 

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