Phospholipase A1 (EC 3.1.1.32; systematic name: phosphatidylcholine 1-acylhydrolase) encoded by the PLA1A gene is a phospholipase enzyme which removes the 1-acyl group: phosphatidylcholine + H2O = 2-acylglycerophosphocholine + a carboxylate It is an enzyme that resides in a class of enzymes called phospholipase that hydrolyze phospholipids into fatty acids. There are four classes, separated according to the type of reaction they catalyze. In particular, phospholipase A1 (PLA1) specifically catalyzes the cleavage at the sn-1 position of phospholipids, forming a fatty acid and a lysophospholipid. Function PLA1's are present in numerous species including humans, and have a variety of cellular functions that include regulation and facilitation of the production of lysophospholipid mediators, and acting as digestive enzymes. These enzymes are responsible for fast turnover rates of cellular phospholipids. In addition to this, the products of the reaction catalyzed by PLA1 which are a fatty acid and a lysophospholipid are important in various biological functions such as platelet aggregation and smooth muscle contraction. In addition, lysophospholipids can be found as surfactants in food techniques and cosmetics, and can be used in drug delivery. Since PLA1 is found in many species, it has been found that there are different classes of this one specific enzyme based on the organism being studied. Species and tissue distribution There are many variations of PLA1, differing slightly between each organism it is present in. Most notably, it can be found in mammalian cells such as plasma of rat livers and bovine brains, and can also be found in metazoan parasites, protozoan parasites, and snake venom. Substrate specificity PLA1 hydrolyzes nonionic substrates preferentially over ionic substrates. Optimum pH conditions for PLA1 activity on neutral phospholipids is around 7.5, whereas the optimal conditions for PLA1 activity on acidic phospholipids is around 4. Structure The structure of a PLA1 is a monomer that contains the following sequence: Gly-X-Ser-X-Gly, where X represents any other amino acid. The serine is considered the active site in the enzyme. PLA1's also contain a catalytic triad of Ser-Asp-His, with a variety of cysteine residues needed for disulfide bond formation. The cysteine residues are responsible for key structural motifs such as the lid domain and the B9 domain, both of which are lipid binding surface loops. These two loops can vary between each PLA1. For example, a PLA1 enzyme with a long lid domain (22-23 amino acids) and a long B9 domain (18-19 amino acids) constitute