The subcellular location of the enzymes of eicosanoid biosynthesis is critical for their co-ordinate action in the generation of leukotrienes and prostaglandins. This activity is thought to occur predominantly at a perinuclear location. Whereas the subcellular locations of cytosolic phospholipase (PL) A2 and each of the pathway enzymes of eicosanoid generation have been defined, the distribution of the low molecular weight species of PLA2 has remained elusive because of the lack of antibodies that distinguish among homologous family members. We have prepared affinity- purified rabbit antipeptide IgG antibodies that distinguish mouse group IIA PLA2 and group V PLA2. Immunofluorescence staining and immunogold electron microscopy reveal different subcellular locations for the enzymes. Group IIA2 PLA2 is present in the secretory granules of mouse bone marrow-derived mast cells, consistent with its putative role in facilitating secretory granule exocytosis and its consequent extracellular action. In contrast, group V PLA2 is associated with various membranous organelles including the Golgi apparatus, nuclear envelope, and plasma membrane. The perinuclear location of group V PLA2 is consistent with a putative interaction with translocated cytosolic PLA2 in supplying arachidonic acid for generation of eicosanoid products, while the location in Golgi cisternae may also reflect its action as a secreted enzyme. The spatial segregation of group IIA PLA2 and group V PLA2 implies that these enzymes are not functionally redundant.
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