Lipases perform essential roles in the digestion, transport and processing of dietary lipids (e.g. triglycerides, fats, oils) in most, if not all, living organisms. Genes encoding lipases are even present in certain viruses.
Most lipases act at a specific position on the glycerol backbone of lipid substrate (A1, A2 or A3)(small intestine). For example, human pancreatic lipase (HPL), which is the main enzyme that breaks down dietary fats in the human digestive system, converts triglyceride substrates found in ingested oils to monoglycerides and two fatty acids.
Some lipases are expressed and secreted by pathogenic organisms during the infection. In particular, Candida albicans has a large number of different lipases, possibly reflecting broad lipolytic activity, which may contribute to the persistence and virulence of C. albicans in human tissue.
Structure and catalytic mechanism
Although 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 (see image) and employ a chymotrypsin-like hydrolysis mechanism involving a serine nucleophile, an acid residue (usually aspartic acid), and a histidine.
Lipases are involved in diverse biological processes ranging from routine metabolism of dietary triglycerides to cell signaling and inflammation. Thus, some lipase activities are confined to specific compartments within cells while others work in extracellular spaces.
- Other lipase enzymes, such as pancreatic lipases, are secreted into extracellular spaces where they serve to process dietary lipids into more simple forms that can be more easily absorbed and transported throughout the body.
- Fungi and bacteria may secrete lipases to facilitate nutrient absorption from the external medium (or in examples of pathogenic microbes, to promote invasion of a new host).
- Certain wasp and bee venoms contain phospholipases that enhance the "biological payload" of injury and inflammation delivered by a sting.
- As biological membranes are integral to living cells and are largely composed of phospholipids, lipases play important roles in cell biology.
- Malassezia globosa, a fungus that is thought to be the cause of human dandruff, uses lipase to break down sebum into oleic acid and increase skin cell production, causing dandruff.
The main lipases of 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).
|bile salt-dependent lipase||bsdl||pancreas, breast milk||aids in the digestion of fats|
|pancreatic lipase||PNLIP||digestive juice||In order to exhibit optimal enzyme activity in the gut lumen, HPL requires another protein, colipase, which is also secreted by the pancreas.|
|lysosomal lipase||LIPA||interior space of organelle: lysosome||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.|
|hepatic lipase||LIPC||endothelium||Hepatic lipase acts on the remaining lipids carried on lipoproteins in the blood to regenerate LDL (low density lipoprotein).||-|
|lipoprotein lipase||LPL or "LIPD"||endothelium||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.|
|gastric lipase||LIPF||digestive juice||Functions in the infant at a near-neutral pH to aid in the digestion of lipids||-|
|pancreatic lipase related protein 2||PNLIPRP2 or "PLRP2" -||digestive juice||-||-|
|pancreatic lipase related protein 1||PNLIPRP1 or "PLRP1"||digestive juice||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.||-|
|lingual lipase||?||digestive juice||Active at gastric pH levels. Optimum pH is about 3.5-6. Secreted by the Parotid and Ebner's glands at the back of the tongue.||-|
There also are a diverse array of phospholipases, but these are not always classified with the other lipases.
Lipases 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 in alternative energy strategies to convert vegetable oil into fuel.High enzyme activity lipase can replace traditional catalyst in processing biodiesel, as this enzyme replaces chemicals in a process with is otherwise highly energy intensive, and can be more environmentally friendly and safe. Industrial application of lipases requires process intensification for continuous processing using tools like continuous flow microreactors at small scale.  Lipases are generally animal sourced, but can also be sourced microbially.
Blood tests for lipase may be used to help investigate and diagnose acute pancreatitis and other disorders of the pancreas. Measured serum lipase values may vary depending on the method of analysis.
General formula of a carboxylate ester
- Alpha toxin
- Lysosomal acid lipase deficiency
- Peripheral membrane proteins
- Phospholipase A
- Phospholipase C
- Triglyceride lipase
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