Aliphatic esterases, PLA1 and PLA2, that release fatty acids from phospholipids. Phosphatidic acid-selective phospholipase A1 (lipase H, 451 aa) generates lysophosphatidic acid and is mutated in autosomal recessive hypotrichosis. PLA1-α (456 aa) acts specifically on phosphatidylserine. Phospholipases A2 (EC 18.104.22.168) are diverse, with secreted, cytosolic, and lipoprotein-associated classes. They are divided into groups: Group I includes pancreatic, PLA2G1B, and is also found in the venom of cobras and kraits; group II are extracellular and require calcium, examples are found in synovial fluid (PLA2G2A) and in the venom of rattlesnakes and vipers; group III is found in bee and lizard venom; group IV are cytosolic and will generate arachidoic acid, the precursor for eicosanoids, and are therefore important in inflammation. A number of other groups are recognized and have differing substrate specificities or tissue distributions. Lipoprotein-associated PLA2s (group VII, EC 22.214.171.124, lp-PLA2) hydrolyse platelet activating factor and deficiency increases susceptibility to asthma and atopy. PLA2G6 (806 aa) is a calcium-independent PLA2 mutated in infantile neuroaxonal dystrophy and Karak's syndrome. A PLA2 receptor has been described (1465 aa) and may be involved in internalizing secreted forms of the enzyme for degradation. Phospholipase A2-activating protein (PLAP, 738 aa) from monocytes may modulate the availability of substrate for eicosanoid synthesis. Various patatin-like phospholipase domain-containing proteins are also known and are intracellular, calcium-independent enzymes with PLA2-like activity implicated in regulation of adipocyte differentiation and are responsive to metabolic demand (see PNPLA6).
Subjects: Medicine and Health.