Multiple forms of phosphoinositide-specific phospholipase C of different relative molecular masses in animal tissues. Evidence for modification of the platelet enzyme by Ca2+-dependent proteinase

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Abstract
The MW distribution of phosphoinositide-specific phospholipase C in the supernatants isolated from a variety of animal tissues was analyzed by high-performance gel-filtration chromatography. In most tissues, at least 4 peaks of activity were resolved. However, different tissues showed quite marked differences in the distribution of activity between these peaks. In rat heart, lung and kidney, the predominant form had MW .apprx. 90,000, whereas the predominant form in brain had MW .apprx. 290,000. In liver, the MW-90,000 form predominated, but this tissue also contained relatively large amounts of a form of MW .apprx. 150,000. Phospholipase C in these tissues from other animal species gave similar distributions of activity between the peaks. In supernatants prepared from platelets sonicated in the presence of leupeptin (0.5 mM) or EGTA [ethylene glycol bis(.beta.-aminoethyl ether)-N,N,N'',N''-tetraacetic acid] (20 mM), the MW-290,000 form predominated. However, when leupeptin or EGTA (inhibitors of Ca2+-dependent proteinase) was omitted from the sonication buffer, the MW-290,000 form appeared to be replaced by a form of MW 100,000. Similar changes in MW were not demonstrated with the other tissues. These results may be relevant to the intracellular regulation of phospholipase C, since Ca2+- dependent proteolysis has been reported to occur during platelet activation.