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Inositol Phospholipid Hydrolysis by Rat Sciatic Nerve Phospholipase C
Author(s) -
Natarajan V.,
Schmid Harald H. O.
Publication year - 1987
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1111/j.1471-4159.1987.tb02450.x
Subject(s) - phosphomonoesterase , chemistry , phospholipase c , inositol , hydrolysis , inositol phosphate , biochemistry , phosphatidylinositol , phospholipid , phosphodiesterase , diacylglycerol kinase , phospholipase , phosphate , phosphatidylcholine , chromatography , phosphatase , enzyme , membrane , protein kinase c , receptor , kinase
Rat sciatic nerve cytosol contains a phosphodiesterase of the phospholipase C type that catalyzes the hydrolysis of inositol phospholipids, with preferences of phospha‐tidylinositol 4′‐phosphate (PIP) > phosphatidylinositol (PI) « phosphatidylinositol 4′, 5′‐bisphosphate (PIP2), at a pH optimum of 5.5–6.0 and at maximum rates of 55, 13, and 0.7 nmol/min/mg protein, respectively. Analysis of reaction products by TLC and formate exchange chromatography shows that inositol 1, 2‐cyclic phosphate (83%) and diacylglycerol are the major products of PI hydrolysis. [ 32 P]PIP hydrolysis yields inositol bisphosphate, inositol phosphate, and inorganic phosphate, indicating the presence of phosphodiesterase, phosphomonoesterase, and/or inositol phosphate phosphatase activities in nerve cytosol. Phosphodiesterase activity is Ca 2+ ‐dependent and completely inhibited by EGTA, but phosphomonoesterase activity is independent of divalent cations or chelating agents. Phosphatidylcholine (PC) and lysophosphatidylcholine (ly‐soPC) inhibit PI hydrolysis. They stimulate PIP and PIP 2 hydrolysis up to equimolar concentrations, but are inhibitory at higher concentrations. Both diacylglycerols and free fatty acids stimulate PI hydrolysis and counteract its inhibition by PC and lysoPC. PIP 2 is a poor substrate for the cytosolic phospholipase C and strongly inhibits hydrolysis of PI. However, it enhances PIP hydrolysis up to an equimolar concentration.