Phospholipases and acyltransferases in macrophages.

In contrast to many other cells, macrophages contain a phospholipase A2, which preferentially liberates arachidonic acid from the main phospholipids. In unstimulated macrophages this acylchain-specific phospholipase A2 is localized in the lipid-free cytosol and thus without function. After activation of protein kinase C with diacylglycerols, the cytosolic phospholipase A2 is translocated to cellular membranes. The same activator of protein kinase C causes an inhibition of the acyl-CoA: lysophosphatide acyltransferase. This enzyme regulates the availability of free arachidonic acid for eicosanoid synthesis by reacylation into phospholipids. Thus protein kinase C seems to regulate the level of free arachidonic acid by opposite effects on the two major enzymes, which are responsible for the control of free arachidonic acid.