Specific phospholipases degrade membrane phospholipids
Most cells continually degrade and replace their membrane lipids. For each of the bonds in a glycerophospholipid there is a specific hydrolitic enzyme.
Phospholipases of the A type remove one of the two fatty acids, producing a lysophospholipid; these esterases do not attack the ether link in plasmalogens. Lysophospholipases remove the remaining fatty acid.
Phospholipids breakdown is a part of at least two signaling processes in animal cells. Extracellular signals (certain hormones, for example) activate a phospholipase C that specifically cleaves phosphatidylinositols , releasing dyacilglicerol and inositol phosphates, which serve as intracellular signal. Other extracellular stimuli activate a phospholipase A that release arachidonic acid from membrane lipids; arachidonate serves as a precursor in the synthesis of the eicosanoids that act as intracellular messengers.
Phospholipases are a group of enzymes that hydrolyze phospholipids into fatty acids and other lipophilic molecules.
PLA is subdivided into PLA1 which cleave phospholipids at the sn-1 ester bond and PLA2, which cleave at the sn-2 bond.
Their most common substrate is phosphatidylcholine, which generates lysophosphatidylcholine and arachidonic acid.
PLA is regulated by phosphorylation and by intracellular Ca2+ concentrations.
Phospholipases are ubiquitously expressed and have diverse biological functions including roles in inflammation, cell growth, signaling and death and maintenance of membrane phospholipids.
Phospholipase A2 specifically recognizes the sn-2 acyl bond of phospholipids and catalytically hydrolyzes the bond releasing arachidonic acid and lysophospholipids.
