lipase: Definition and Much More from Answers.com
- ️Wed Jul 01 2015
A lipase is a water-soluble enzyme that catalyzes the hydrolysis of ester bonds in water–insoluble, lipid substrates[1]. Lipases thus comprise a subclass of the esterases.
Lipases are ubiquitous throughout living organisms, and genes encoding lipases are even present in certain viruses. [2][3]
Function
Most lipases act at a specific position on the glycerol backbone of a lipid substrate (A1, A2 or A3).
In the example of human pancreatic lipase (HPL)[4], which is the main enzyme responsible for breaking down fats in the human digestive system, a lipase acts to convert triglyceride substrates found in oils from food to monoglycerides and free fatty acids.
Myriad other lipase activities exist in nature, especially when the phospholipases[5] and sphingomyelinases[6] are considered.
Structure
While a diverse array of genetically distinct lipase enzymes are found in nature, and represent several types of protein folds and catalytic mechanisms, most are built on an alpha/beta hydrolase fold [7][8][9] (see image[10]) and employ a chymotrypsin-like hydrolysis mechanism involving a serine nucleophile, an acid residue (usually aspartic acid), and a histidine[11][12].
Location of action
Some lipases work within the interior spaces of living cells to degrade lipids.
- Other lipase enzymes, such as pancreatic lipases, are found in the spaces outside of cells and have roles in the metabolism, absorption and transport of lipids throughout the body.
As biological membranes are integral to living cells and are largely composed of phospholipids, lipases play important roles in cell biology.
Furthermore, lipases are involved in diverse biological processes ranging from routine metabolism of dietary triglycerides to cell signaling[13] and inflammation[14].
Lipases of Humans
The main lipases in the human digestive system are human pancreatic lipase (HPL) and pancreatic lipase related protein 2 (PLRP2), which are secreted by the pancreas. Humans also have several other related enzymes, including hepatic lipase (HL), endothelial lipase, and lipoprotein lipase. Not all of these lipases function in the gut (see table).
| Name | Gene | Description | Disorder |
| pancreatic lipase | PNLIP | In order to exhibit optimal enzyme activity in the gut lumen, HPL requires another protein, colipase, which is also secreted by the pancreas[15]. | - |
| lysosomal lipase | LIPA | Also referred to as lysosomal acid lipase (LAL or LIPA) or acid cholesteryl ester hydrolase | Cholesteryl ester storage disease (CESD) and Wolman disease are both caused by mutations in the gene encoding lysosomal lipase.[16] |
| hepatic lipase | LIPC | Hepatic lipase acts on the remaining lipids carried on lipoproteins in the blood to regenerate LDL (low density lipoprotein). | - |
| lipoprotein lipase | LPL or "LIPD" | Lipoprotein lipase functions in the blood to act on triacylglycerides carried on VLDL (very low density lipoprotein) so that cells can take up the freed fatty acids. | Lipoprotein lipase deficiency is caused by mutations in the gene encoding lipoprotein lipase.[17] [18] |
| hormone-sensitive lipase | LIPE | - | - |
| gastric lipase | LIPF | Functions in the infant at a near-neutral pH to aid in the digestion of lipids | - |
| endothelial lipase | LIPG | - | - |
| pancreatic lipase related protein 2 | PNLIPRP2 or "PLRP2" | - | - |
| pancreatic lipase related protein 1 | PNLIPRP1 or "PLRP1" | Pancreatic lipase related protein 1 is very similar to PLRP2 and HPL by amino acid sequence (all three genes probably arose via gene duplication of a single ancestral pancreatic lipase gene). However, PLRP1 is devoid of detectable lipase activity and its function remains unknown, even though it is conserved in other mammals[19][20]. | - |
Other lipases include LIPH, LIPI, LIPJ, LIPK, LIPM, and LIPN.
There also are a diverse array of phospholipases, but these are not always classified with the other lipases.
Industrial Uses
Lipases from fungi and bacteria serve important roles in human practices as ancient as yogurt and cheese fermentation. However, lipases are also being exploited as cheap and versatile catalysts to degrade lipids in more modern applications. For instance, a biotechnology company has brought recombinant lipase enzymes to market for use in applications such as baking, laundry detergents and even as biocatalysts [21] in alternative energy strategies to convert vegetable oil into fuel. [22][23]
Additional images
References
External links
- MeSH Lipase
- Selective Inhibitors of Monoacylglycerol Lipase as a Treatment for Neurological Disorders 2004-637
- UMich Orientation of Proteins in Membranes families/superfamily-90 - Phospholipases A2
- UMich Orientation of Proteins in Membranes families/superfamily-29 - Outer membrane phospholipase A
- UMich Orientation of Proteins in Membranes families/superfamily-134 - Cytosolic phospholipase A2 and patatin
- UMich Orientation of Proteins in Membranes families/superfamily-126 - Bacterial and mammalian phospolipases C
- UMich Orientation of Proteins in Membranes families/superfamily-88 - α-toxin (a bacterial phospholipase C)
See also
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