A phospholipase is an enzyme that hydrolyzes
phospholipid
Phospholipids, are a class of lipids whose molecule has a hydrophilic "head" containing a phosphate group and two hydrophobic "tails" derived from fatty acids, joined by an alcohol residue (usually a glycerol molecule). Marine phospholipids typ ...
s into
fatty acid
In chemistry, particularly in biochemistry, a fatty acid is a carboxylic acid with an aliphatic chain, which is either saturated or unsaturated. Most naturally occurring fatty acids have an unbranched chain of an even number of carbon atoms, fr ...
s and other
lipophilic
Lipophilicity (from Greek λίπος "fat" and φίλος "friendly"), refers to the ability of a chemical compound to dissolve in fats, oils, lipids, and non-polar solvents such as hexane or toluene. Such non-polar solvents are themselves lipop ...
substances. Acids trigger the release of bound calcium from cellular stores and the consequent increase in free cytosolic Ca
2+, an essential step in calcium signaling to regulate intracellular processes. 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
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 ...
– cleaves the ''sn''-1
acyl chain (where ''sn'' refers to
stereospecific numbering).
**
Phospholipase A2
The enzyme phospholipase A2 (EC 3.1.1.4, PLA2, systematic name phosphatidylcholine 2-acylhydrolase) catalyse the cleavage of fatty acids in position 2 of phospholipids, hydrolyzing the bond between the second fatty acid “tail” and the glyce ...
– cleaves the ''sn''-2
acyl chain, releasing
arachidonic acid
Arachidonic acid (AA, sometimes ARA) is a polyunsaturated omega-6 fatty acid 20:4(ω-6), or 20:4(5,8,11,14). It is structurally related to the saturated arachidic acid found in cupuaçu butter. Its name derives from the New Latin word ''arachi ...
.
*
Phospholipase B – cleaves both ''sn''-1 and ''sn''-2
acyl chains; this enzyme is also known as a lysophospholipase.
*
Phospholipase C
Phospholipase C (PLC) is a class of membrane-associated enzymes that cleave phospholipids just before the phosphate group (see figure). It is most commonly taken to be synonymous with the human forms of this enzyme, which play an important role ...
– cleaves before the phosphate, releasing
diacylglycerol
A diglyceride, or diacylglycerol (DAG), is a glyceride consisting of two fatty acid chains covalently bonded to a glycerol molecule through ester linkages. Two possible forms exist, 1,2-diacylglycerols and 1,3-diacylglycerols. DAGs can act as sur ...
and a phosphate-containing head group.
PLCs play a central role in
signal transduction
Signal transduction is the process by which a chemical or physical signal is transmitted through a cell as a series of molecular events, most commonly protein phosphorylation catalyzed by protein kinases, which ultimately results in a cellula ...
, releasing the
second messenger
Second messengers are intracellular signaling molecules released by the cell in response to exposure to extracellular signaling molecules—the first messengers. (Intercellular signals, a non-local form or cell signaling, encompassing both first me ...
inositol triphosphate
Inositol trisphosphate or inositol 1,4,5-trisphosphate abbreviated InsP3 or Ins3P or IP3 is an inositol phosphate signaling molecule. It is made by hydrolysis of phosphatidylinositol 4,5-bisphosphate (PIP2), a phospholipid that is located in the p ...
.
*
Phospholipase D – cleaves after the phosphate, releasing
phosphatidic acid Phosphatidic acids are anionic phospholipids important to cell signaling and direct activation of lipid-gated ion channels. Hydrolysis of phosphatidic acid gives rise to one molecule each of glycerol and phosphoric acid and two molecules of fatty ac ...
and an alcohol.
Types C and D are considered
phosphodiesterase
A phosphodiesterase (PDE) is an enzyme that breaks a phosphodiester bond. Usually, ''phosphodiesterase'' refers to cyclic nucleotide phosphodiesterases, which have great clinical significance and are described below. However, there are many oth ...
s.
Endothelial lipase
Endothelial lipase (LIPG) is a form of lipase secreted by vascular endothelial cells in tissues with high metabolic rates and vascularization, such as the liver, lung, kidney, and thyroid gland. The LIPG enzyme is a vital component to many biologi ...
is primarily a phospholipase.
Phospholipase A2 acts on the intact lecithin molecule and hydrolyzes the fatty acid esterified to the second carbon atom. The resulting products are
lysolecithin
Lysophosphatidylcholines (LPC, lysoPC), also called lysolecithins, are a class of chemical compounds which are derived from phosphatidylcholines.
Overview
Lysophosphatidylcholines are produced within cells mainly by the enzyme phospholipase ...
and a fatty acid. Phospholipase A2 is an enzyme present in the venom of
bees,
blennies
Blenny (from the Greek and , mucus, slime) is a common name for many types of fish, including several families of percomorph marine, brackish, and some freshwater fish sharing similar morphology and behaviour. Six families are considered "true ...
and
viper snakes.
[D. M. Vasudevan & S. Sreekumari, ''Textbook of Biochemistry'' (5th ed.)]
See also
*
Patatin-like phospholipase
*
Infantile neuroaxonal dystrophy
Infantile neuroaxonal dystrophy is a rare pervasive developmental disorder that primarily affects the nervous system. Individuals with infantile neuroaxonal dystrophy typically do not have any symptoms at birth, but between the ages of about 6 and ...
References
Further reading
* Tappia, Paramjit S. & Dhalla, Naranjan S. (Editors): ''Phospholipases in Health and Disease.'' Springer, 2014.
rint
C mathematical operations are a group of functions in the standard library of the C programming language implementing basic mathematical functions. All functions use floating-point numbers in one manner or another. Different C standards provid ...
Book
A book is a medium for recording information in the form of writing or images, typically composed of many pages (made of papyrus, parchment, vellum, or paper) bound together and protected by a cover. The technical term for this physical arr ...
External links
*
Peripheral membrane proteins
Cell signaling
Hydrolases
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