ISSN:
1573-4919
Keywords:
phospholipase C
;
phosphoinositides
;
phosphatidylinositol 4,5-bisphosphate
;
phosphatidylinositol 4-phosphate
;
rat heart
;
sarcolemma
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
,
Chemistry and Pharmacology
,
Medicine
Notes:
Abstract In rat cardiac sarcolemmal membranes a phosphoinositide-specific phospholipase C (PLC) was found to be present. The enzyme hydrolysed exogenous [3H-]phosphatidylinositol 4,5-biphosphate ([3H-]PtdIns(4,5)P 2) in an optimized assay mixture containing 15 leg SL protein, 100 mM NaCl, 1 mM free Ca2+,14 mM Na-cholate and 20 AM [3H-]PtdIns (4,5)P 2 (400–500 dpm/gm-l) in 30 mM HEPES-Tris buffer (pH 7.0). The average specific activity was 9.14±0.55 nmol-mg−1·2.5 min−1. The addition of Mg2+ to the assay mixture did not change PLC activity but increased the relative amounts of dephosphorylated inositol products. In the absence of Na+ and at a low Ca2+ concentration (0.3 μM), Mg2+ also enhanced the intraSL levels of PtdIns4P and PtdIns, and, moreover, inhibited PLC activity (IC50∼0.07 mM). PtdIns4P seemd to be a good substrate for the rat SL PLC (23.07 ± 1.57 nmol·mg−1·2.5 min−1) whereas PtdIns was hydrolysed at a very low rate (0.36 ± 0.08 nmol·mg−1·2.5 min−1). Unlike PtdIns(4,5)P 2, PLC-dependent PtdIns4P and PtdIns hydrolysis was not inhibited by Ca2+ concentrations over 1 mM. The possibility of distinct isozymes being responsible for the different hydrolytic activities is discussed. (Mol Cell Biochem116: 27–31, 1992).
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF01270565
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