Localization and evolution of two human phospholipase A2 genes and two related genetic elements.

Mammals are now known to contain at least two distinct classes of phospholipases A2, the progenitors of which can be seen in the venoms of snakes. Mammalian "Type I" PLA2, synthesized primarily by the pancreas, is also present in smaller amounts in other tissues including lung, spleen, and kidney. Recently, a mammalian "Type II" PLA2 has been sequenced, and shown to occur in platelets, synovial cells and fluid, cells of inflammatory peritoneal exudate, liver, intestine, kidney, and placenta. This form, referred to here as Type IIA PLA2, could play a key role in arachidonate release in both normal and pathologic inflammation. The genes encoding both forms have also been recently cloned. Here, the sites of synthesis and respective roles of the two known enzymes are discussed, along with an analysis of the evolutionary conservation of Type IIA PLA2 gene sequence. In addition, two related genetic elements containing sequences homologous to a portion of Type II PLA2 are described, which map to the same chromosome as the Type IIA PLA2 gene (chromosome 1). Either or both of these could also encode a portion of additional mammalian PLA2s.