Phospholipase

A phospholipase is an enzyme that hydrolyzes phospholipids[1] into fatty acids and other lipophilic substances. Acids trigger the release of bound calcium from cellular stores and the consequent increase in free cytosolic Ca²⁺, an essential step in calcium signaling to regulate intracellular processes.[2] There are four major classes, termed A, B, C, and D, which are distinguished by the type of reaction which they catalyze:

• Phospholipase A
  • Phospholipase A1 – cleaves the sn-1 acyl chain (where sn refers to stereospecific numbering).
  • 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. PLCs 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.

Phospholipase cleavage sites. An enzyme that displays both PLA1 and PLA2 activities is called a Phospholipase B.

Types C and D are considered phosphodiesterases.

Endothelial lipase is primarily a phospholipase.[3]

Phospholipase A2 acts on the intact lecithin molecule and hydrolyzes 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, blennies and viper snakes.[4]