The localization of phospholipase A2 in the secretory granule.
A heat-resistant phospholipase A2 has been detected in the secretory granules of the mast cell [Chock, Rhee, Tang and Schmauder-Chock (1991) Eur. J. Biochem. 195, 707-713]. By using ultrastructural immunocytochemical techniques, we have now localized this enzyme to the matrix of the secretory granule. Like the cyclo-oxygenase [Schmauder-Chock and Chock (1989) J. Histochem. Cytochem. 37, 1319-1328], this enzyme also adheres tightly to the ribbon-like granule matrix components. The results from Western-blot analysis suggest that it has a molecular mass of about 14 kDa. The localization of the phospholipase A2, the presence of a phospholipid store with millimolar concentrations of calcium and the localization of the enzymes of the arachidonic acid cascade make the secretory granule a natural site for lipid-mediator synthesis. The packaging of phospholipase A2, together with its substrate and the components of the arachidonic acid cascade, in the secretory granule represents a physical arrangement by which the initiation of the cascade and the release of mediators can be directly linked to the stimulation of cell-surface receptors.
Department of Biochemistry and Molecular Biology, Howard University School of Medicine, Washington, DC 20059.
S P
SP
Chock
E A
EA
Schmauder-Chock
E
E
Cordella-Miele
L
L
Miele
A B
AB
Mukherjee
D000818:Animals; D003594:Cytoplasmic Granules / Q000201:enzymology* / Q000648:ultrastructure; D007158:Immunologic Techniques; D008407:Mast Cells / Q000201:enzymology* / Q000648:ultrastructure; D008854:Microscopy, Electron; D008970:Molecular Weight; D010741:Phospholipases A / Q000378:metabolism*; D054467:Phospholipases A2; D051381:Rats
D010741:Phospholipases A; D054467:Phospholipases A2