Lipase

A lipase (/ˈlaɪpeɪs/, /-peɪz/) is any enzyme that catalyzes the hydrolysis of fats (lipids).[1] Lipases are a subclass of the esterases.

A computer-generated image of a type of pancreatic lipase (PLRP2) from the guinea pig. PDB: 1GPL​.

Lipases perform essential roles in 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.[2][3]

Most lipases act at a specific position on the glycerol backbone of a lipid substrate (A1, A2 or A3)(small intestine). For example, human pancreatic lipase (HPL),[4] 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.

Several other types of lipase activities exist in nature, such as phospholipases [5] and sphingomyelinases;[6] however, these are usually treated separately from "conventional" lipases.

Some lipases are expressed and secreted by pathogenic organisms during an infection. In particular, Candida albicans has many different lipases, possibly reflecting broad-lipolytic activity, which may contribute to the persistence and virulence of C. albicans in human tissue.[7]

Structure and catalytic mechanism

A diverse array of genetically distinct lipase enzymes are found in nature, and they represent several types of protein folds and catalytic mechanisms. However, most are built on an alpha/beta hydrolase fold[8][9][10][11] and employ a chymotrypsin-like hydrolysis mechanism using a catalytic triad consisting of a serine nucleophile, a histidine base, and an acid residue, usually aspartic acid.[12][13]

Physiological distribution

Lipases are involved in diverse biological processes which range from routine metabolism of dietary triglycerides to cell signaling[14] and inflammation.[15] Thus, some lipase activities are confined to specific compartments within cells while others work in extracellular spaces.

  • In the example of lysosomal lipase, the enzyme is confined within an organelle called the lysosome.
  • 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 effects 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 thought to be the cause of human dandruff, uses lipase to break down sebum into oleic acid and increase skin cell production, causing dandruff.[16]

Human lipases

The main lipases of the human digestive system are pancreatic lipase (PL) and pancreatic lipase related protein 2 (PLRP2), which are secreted by the pancreas. Humans also have several related enzymes, including hepatic lipase, endothelial lipase, and lipoprotein lipase. Not all of these lipases function in the gut (see table).

NameGeneLocationDescriptionDisorder
bile salt-dependent lipasebsdlpancreas, breast milkaids in the digestion of fats
pancreatic lipasePNLIPdigestive juiceIn order to exhibit optimal enzyme activity in the gut lumen, PL requires another protein, colipase, which is also secreted by the pancreas.[17]
lysosomal lipaseLIPAinterior space of organelle: lysosomeAlso referred to as lysosomal acid lipase (LAL or LIPA) or acid cholesteryl ester hydrolaseCholesteryl ester storage disease (CESD) and Wolman disease are both caused by mutations in the gene encoding lysosomal lipase.[18]
hepatic lipaseLIPCendotheliumHepatic lipase acts on the remaining lipids carried on lipoproteins in the blood to regenerate LDL (low density lipoprotein).–
lipoprotein lipaseLPL or "LIPD"endotheliumLipoprotein 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.[19][20]
hormone-sensitive lipaseLIPEintracellular––
gastric lipaseLIPFdigestive juiceFunctions in the infant at a near-neutral pH to aid in the digestion of lipids–
endothelial lipaseLIPGendothelium––
pancreatic lipase related protein 2PNLIPRP2 or "PLRP2" –digestive juice––
pancreatic lipase related protein 1PNLIPRP1 or "PLRP1"digestive juicePancreatic lipase related protein 1 is very similar to PLRP2 and PL 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.[21][22]-
lingual lipase?salivaActive at gastric pH levels. Optimum pH is about 3.5-6. Secreted by several of the salivary glands (Ebner's glands at the back of the tongue (lingua), the sublingual glands, and the parotid glands)–

Other lipases include LIPH, LIPI, LIPJ, LIPK, LIPM, LIPN, MGLL, DAGLA, DAGLB, and CEL.

There also are a diverse array of phospholipases, but these are not always classified with the other lipases.

Industrial uses

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[23] in alternative energy strategies to convert vegetable oil into fuel.[24][25] High enzyme activity lipase can replace traditional catalyst in processing biodiesel, as this enzyme replaces chemicals in a process which is otherwise highly energy intensive,[26] 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.[27][28] Lipases are generally animal sourced, but can also be sourced microbially.

Diagnostic use

Blood tests for lipase may be used to help investigate and diagnose acute pancreatitis and other disorders of the pancreas.[29] Measured serum lipase values may vary depending on the method of analysis.

Medical use

Lipase can also assist in the breakdown of fats into lipids in those undergoing pancreatic enzyme replacement therapy (PERT). It is a key component in Sollpura (Liprotamase).[30][31]

Additional images
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See also

References
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  16. Genetic Code of Dandruff Cracked – BBC News
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  18. Omim – Wolman Disease
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25. Gulzar, Bio-degradation of hydrocarbons using different bacterial and fungal species. Published in international conference on biotechnology and neurosciences. CUSAT (cochin university of science and technology), 2003

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