Purification and Assay of Mammalian Group I and Group IIa Secretory Phospholipase A2

Phospholipases A₂ (PLA₂ ) are a family of ubiquitous lipolytic enzymes that are found both as intracellular and secreted proteins. Secretory PLA₂ s are small (14 kDa), homologous proteins that require millimolar Ca²⁺ for catalytic activity. They can be classified into at least four groups based on minor structural differences (1 ,2 ). In particular, two major classes of highly homologous secretory enzymes (class I and IIa) have been found in mammalian tissues. Mammalian class I PLA₂ s are synthesized in the pancreas as pro-enzymes and activated by proteolytic cleavage in the intestine (for review see ref. 3 and references therein). All known mammalian pancreatic PLA₂ s show strong sequence homology. The main function of these pancreatic PLA₂ s is to digest dietary phospholipids emulsified with bile juice (3 ). Recently, several lines of evidence have indicated that mammalian pancreatic PLA₂ s are present in different tissues and might play other physiological roles, including cell surface receptor-mediated inflammation (4 ).