GROUP-SPECIFIC ASSAYS THAT DISTINGUISH BETWEEN THE FOUR MAJOR TYPES OF MAMMALIAN PHOSPHOLIPASE A2

Abstract Phospholipase A 2 (PLA 2 ) constitutes a diverse superfamily of enzymes which catalyze the deacylation of phospholipids. At least four types of PLA 2 are potentially involved in arachidonic acid release in cells and tissues. Since all of them catalyze the same enzymatic reaction, it is difficult to distinguish between them in mixtures of enzymes normally present in biological samples. Utilizing specific properties of each PLA 2 , we have designed distinct assay procedures which selectively and sensitively detect each type: Group VI Ca 2+ -independent PLA 2 , Group IV cytosolic Ca 2+ -dependent PLA 2 , Groups V and IIA secreted PLA 2 s. Each specific assay procedure is selective for a particular PLA 2 type by at least fourfold and as high as four orders of magnitude relative to the other three enzymes. All assays can detect PLA 2 activity with as low as subnanogram quantities of enzyme. Importantly, these assays are able to differentiate and quantitate the biochemically and structurally related enzymes, Group IIA and V sPLA 2 s in crude biological samples. Employing this system, we have found that iPLA 2 is the dominant PLA 2 in rat brain, and cPLA 2 is the most abundant PLA 2 in P388D 1 macrophages and human amnionic WISH cells.