Arachidonic acid is a polyunsaturated omega−6 fatty acid 20:4(ω−6), or 20:4(5,8,11,14). If its precursors or diet contains linoleic acid it is formed by biosynthesis and can be deposited in animal fats. It is a precursor in the formation of leukotrienes, prostaglandins, and thromboxanes.
Fatty acid metabolism consists of various metabolic processes involving or closely related to fatty acids, a family of molecules classified within the lipid macronutrient category. These processes can mainly be divided into (1) catabolic processes that generate energy and (2) anabolic processes where they serve as building blocks for other compounds.
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 acids. They constitute about 0.25% of phospholipids in the bilayer.
The enzyme phospholipase A2 (EC 3.1.1.4, PLA2, systematic name phosphatidylcholine 2-acylhydrolase) catalyses the cleavage of fatty acids in position 2 of phospholipids, hydrolyzing the bond between the second fatty acid "tail" and the glycerol molecule:
Glycerophospholipids or phosphoglycerides are glycerol-based phospholipids. They are the main component of biological membranes in eukaryotic cells. They are a type of lipid, of which its composition affects membrane structure and properties. Two major classes are known: those for bacteria and eukaryotes and a separate family for archaea.
Lingual lipase is a member of a family of digestive enzymes called triacylglycerol lipases, EC 3.1.1.3, that use the catalytic triad of aspartate, histidine, and serine to hydrolyze medium and long-chain triglycerides into partial glycerides and free fatty acids. The enzyme, released into the mouth along with the saliva, catalyzes the first reaction in the digestion of dietary lipid, with diglycerides being the primary reaction product. However, due to the unique characteristics of lingual lipase, including a pH optimum 4.5–5.4 and its ability to catalyze reactions without bile salts, the lipolytic activity continues through to the stomach. Enzyme release is signaled by autonomic nervous system after ingestion, at which time the serous glands under the circumvallate and foliate lingual papillae on the surface of the tongue secrete lingual lipase to the grooves of the circumvallate and foliate papillae, co-localized with fat taste receptors. The hydrolysis of the dietary fats is essential for fat absorption by the small intestine, as long chain triacylglycerides cannot be absorbed, and as much as 30% of fat is hydrolyzed within 1 to 20 minutes of ingestion by lingual lipase alone.
Lipid signaling, broadly defined, refers to any biological cell signaling event involving a lipid messenger that binds a protein target, such as a receptor, kinase or phosphatase, which in turn mediate the effects of these lipids on specific cellular responses. Lipid signaling is thought to be qualitatively different from other classical signaling paradigms because lipids can freely diffuse through membranes. One consequence of this is that lipid messengers cannot be stored in vesicles prior to release and so are often biosynthesized "on demand" at their intended site of action. As such, many lipid signaling molecules cannot circulate freely in solution but, rather, exist bound to special carrier proteins in serum.
Lipid metabolism is the synthesis and degradation of lipids in cells, involving the breakdown and storage of fats for energy and the synthesis of structural and functional lipids, such as those involved in the construction of cell membranes. In animals, these fats are obtained from food and are synthesized by the liver. Lipogenesis is the process of synthesizing these fats. The majority of lipids found in the human body from ingesting food are triglycerides and cholesterol. Other types of lipids found in the body are fatty acids and membrane lipids. Lipid metabolism is often considered the digestion and absorption process of dietary fat; however, there are two sources of fats that organisms can use to obtain energy: from consumed dietary fats and from stored fat. Vertebrates use both sources of fat to produce energy for organs such as the heart to function. Since lipids are hydrophobic molecules, they need to be solubilized before their metabolism can begin. Lipid metabolism often begins with hydrolysis, which occurs with the help of various enzymes in the digestive system. Lipid metabolism also occurs in plants, though the processes differ in some ways when compared to animals. The second step after the hydrolysis is the absorption of the fatty acids into the epithelial cells of the intestinal wall. In the epithelial cells, fatty acids are packaged and transported to the rest of the body.
Diacylglycerol lipase, also known as DAG lipase, DAGL, or DGL, is an enzyme that catalyzes the hydrolysis of diacylglycerol, releasing a free fatty acid and monoacylglycerol:
diacylglycerol + H2O ⇌ monoacylglycerol + free fatty acid
Acyl-CoA is a group of coenzymes that metabolize carboxylic acids. Fatty acyl-CoA's are susceptible to beta oxidation, forming, ultimately, acetyl-CoA. The acetyl-CoA enters the citric acid cycle, eventually forming several equivalents of ATP. In this way, fats are converted to ATP, the common biochemical energy carrier.
The long chain fatty acyl-CoA ligase is an enzyme of the ligase family that activates the oxidation of complex fatty acids. Long chain fatty acyl-CoA synthetase catalyzes the formation of fatty acyl-CoA by a two-step process proceeding through an adenylated intermediate. The enzyme catalyzes the following reaction,
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:
Serine hydrolases are one of the largest known enzyme classes comprising approximately ~200 enzymes or 1% of the genes in the human proteome. A defining characteristic of these enzymes is the presence of a particular serine at the active site, which is used for the hydrolysis of substrates. The hydrolysis of the ester or peptide bond proceeds in two steps. First, the acyl part of the substrate is transferred to the serine, making a new ester or amide bond and releasing the other part of the substrate is released. Later, in a slower step, the bond between the serine and the acyl group is hydrolyzed by water or hydroxide ion, regenerating free enzyme. Unlike other, non-catalytic, serines, the reactive serine of these hydrolases is typically activated by a proton relay involving a catalytic triad consisting of the serine, an acidic residue and a basic residue, although variations on this mechanism exist.
The enzyme glycosylphosphatidylinositol diacylglycerol-lyase catalyzes the reaction
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 in eukaryotic cell physiology, in particular signal transduction pathways. Phospholipase C's role in signal transduction is its cleavage of phosphatidylinositol 4,5-bisphosphate (PIP2) into diacyl glycerol (DAG) and inositol 1,4,5-trisphosphate (IP3), which serve as second messengers. Activators of each PLC vary, but typically include heterotrimeric G protein subunits, protein tyrosine kinases, small G proteins, Ca2+, and phospholipids.
N-acyl phosphatidylethanolamine phospholipase D (NAPE-PLD) is an enzyme that catalyzes the release of N-acylethanolamine (NAE) from N-acyl-phosphatidylethanolamine (NAPE). This is a major part of the process that converts ordinary lipids into chemical signals like anandamide and oleoylethanolamine. In humans, the NAPE-PLD protein is encoded by the NAPEPLD gene.
In biochemistry, lipase refers to a class of enzymes that catalyzes the hydrolysis of fats. Some lipases display broad substrate scope including esters of cholesterol, phospholipids, and of lipid-soluble vitamins and sphingomyelinases; however, these are usually treated separately from "conventional" lipases. Unlike esterases, which function in water, lipases "are activated only when adsorbed to an oil–water interface". Lipases perform essential roles in digestion, transport and processing of dietary lipids in most, if not all, organisms.
1-Lysophosphatidylcholines are a class of phospholipids that are intermediates in the metabolism of lipids. They result from the hydrolysis of an acyl group from the sn-1 position of phosphatidylcholine. They are also called 2-acyl-sn-glycero-3-phosphocholines. The synthesis of phosphatidylcholines with specific fatty acids occurs through the synthesis of 1-lysoPC. The formation of various other lipids generates 1-lysoPC as a by-product.
N-acetylphosphatidylethanolamine-hydrolysing phospholipase D (EC 3.1.4.54, NAPE-PLD, anandamide-generating phospholipase D, N-acyl phosphatidylethanolamine phospholipase D, NAPE-hydrolyzing phospholipase D) is an enzyme with systematic name 'N-acetylphosphatidylethanolamine phosphatidohydrolase. It catalyses the following chemical reaction
Lipase inhibitors belong to a drug class that is used as an antiobesity agent. Their mode of action is to inhibit gastric and pancreatic lipases, enzymes that play an important role in the digestion of dietary fat. Lipase inhibitors are classified in the ATC-classification system as A08AB . Numerous compounds have been either isolated from nature, semi-synthesized, or fully synthesized and then screened for their lipase inhibitory activity but the only lipase inhibitor on the market is orlistat . Lipase inhibitors have also shown anticancer activity, by inhibiting fatty acid synthase.
