Phospholipases of the myocardium.
The myocardium contains diverse cellular components and heterogeneous phospholipid-containing membranes. The major phospholipids are phosphatidylcholine, phosphatidylethanolamine, phosphatidylinositnol, sphingomyelin and cardiolipin. The phospholipases capable of hydrolyzing these membrane lipids include phospholipase A, lysophospholipase, and phosphatidylnositol-specific phospholipase C. Early studies revealed that myocardial phospholipase A with an acid pH is localized to lysosomes; those with more alkaline and neutral activities are present in cytosol, microsomes, mitochondria and sarcolemma. Recently, we have identified phosphatidylinositol-specific phospholipase C activity in bovine myocardium with molecular weights ranging from 40,000 to 271,000. Interestingly, forms I, II and III, had pH optima ranging from 4.5 to 5.5; form III also had significant activity at pH 7.0. All activities were stimulated by calcium, suggesting that they are different from calcium-independent phospholipases C found in liver and brain. The pathophysiological significance of these four cytosolic forms of phospholipase C remains to be determined. Thus, under injury-promoting conditions, phospholipase C appears capable of hydrolyzing membrane-associated phosphatidylinositol and the polyphosphoinositides, whereas phospholipases A and lysophospholiphases appear to prefer non-inositol containing phospholipids. Finally, very recent studies suggest "free radical-triggered lipolysis" by phospholipases as a possible mechanism for production of lysophospholipids in myocardial membranes.
Weglicki
W B
WB
Department of Medicine, George Washington University Medical Center, Washington, D. C.
Low
M G
MG
D000818:Animals; D003327:Coronary Disease / Q000201:enzymology; D005609:Free Radicals; D050356:Lipid Metabolism; D008066:Lipolysis; D009206:Myocardium / Q000201:enzymology*; D010740:Phospholipases / Q000378:metabolism*; D010741:Phospholipases A / Q000378:metabolism; D010738:Type C Phospholipases / Q000378:metabolism
D005609:Free Radicals; D010740:Phospholipases; D010741:Phospholipases A; D010738:Type C Phospholipases