Phospholipases
phospholipases
A phospholipase is an enzyme that hydrolyzes phospholipids into fatty acids and other lipophilic substances. There are four major classes, termed A, B, C and D, distinguished by the type of reaction which they catalyze:   Phospholipase A   Phospholipase A1 - cleaves the SN-1 acyl chain.  Phospholipase A2 - cleaves the SN-2 acyl chain, releasing arachidonic acid.    Phospholipase B - cleaves both SN-1 and SN-2 acyl chains ; this enzyme is also known as a lysophospholipase.  Phospholipase C - cleaves before the phosphate, releasing diacylglycerol and a phosphate-containing head group. Phospholipase Cs play a central role in signal transduction, releasing the second messenger inositol triphosphate.  Phospholipase D - cleaves after the phosphate, releasing phosphatidic acid and an alcohol.   Types C and D are considered phosphodiesterases.  Phospholipase A2 acts on the intact lecithin molecule and hydrolyses the fatty acid esterified to the second carbon atom. The resulting products are lysolecithin and a fatty acid. Phospholipase A2 is an enzyme present in the venom of bees and viper snakes.