Low molecular weight group IIA and group V phospholipase A(2) enzymes havedifferent intracellular locations in mouse bone marrow-derived mast cells

The subcellular location of the enzymes of eicosanoid biosynthesis is criti cal for their co-ordinate action in the generation of leukotrienes and pros taglandins. This activity is thought to occur predominantly at a perinuclea r location. Whereas the subcellular locations of cytosolic phospholipase (P L) A(2) and each of the pathway enzymes of eicosanoid generation have been defined, the distribution of the low molecular weight species of PLA(2) has remained elusive because of the lack of antibodies that distinguish among homologous family members. We have prepared affinity-purified rabbit antipe ptide IgG antibodies that distinguish mouse group IIA PLA(2) and group V PL A(2). Immunofluorescence staining and immunogold electron microscopy reveal different subcellular locations for the enzymes. Group IIA(2) PLA(2) is pr esent in the secretory granules of mouse bone marrow-derived mast cells, co nsistent with its putative role in facilitating secretory granule exocytosi s and its consequent extracellular action. In contrast, group V PLA(2) is a ssociated with various membranous organelles including the Golgi apparatus, nuclear envelope, and plasma membrane. The perinuclear location of group V PLA(2) is consistent with a putative interaction with translocated cytosol ic PLA(2) in supplying arachidonic acid for generation of eicosanoid produc ts, while the location in Golgi cisternae may also reflect its action as a secreted enzyme. The spatial segregation of group IIA PLA(2) and group V PL A(2) implies that these enzymes are not functionally redundant.