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

Abstract

Phospholipases A₂ (PLA₂) are a family of ubiquitous lipolytic enzymes that are found both as intracellular and secreted proteins. Secretory PLA₂s 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 PLA₂s 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 PLA₂s show strong sequence homology. The main function of these pancreatic PLA₂s is to digest dietary phospholipids emulsified with bile juice (3). Recently, several lines of evidence have indicated that mammalian pancreatic PLA₂s are present in different tissues and might play other physiological roles, including cell surface receptor-mediated inflammation (4).