Esterases sterol esterase

This enzyme [EC 3.1.1.13] (also known as cholesterol esterase, sterol esterase, cholesterol ester synthase, and triterpenol esterase) catalyzes the hydrolysis of a steryl ester to produce a sterol and a fatty acid anion. This class represents a group of enzymes exhibiting broad specificity. They act on esters of sterols and long-chain fatty acids, and may also bring about the esterification of sterols. These enzymes are typically activated by bile salts. See also Esterases D. P. Hajjar (1994) Adv. Enzymol. 69, 45. 

Sterol esterase Steryl-ester acylhydrolase, cholesterol esterase Steryl esters... 

The overall metabolism of vitamin A in the body is regulated by esterases. Dietary retinyl esters are hydrolyzed enzymatically in the intestinal lumen, and free retinol enters the enterocyte, where it is re-esterified. The resulting esters are then packed into chylomicrons delivered via the lymphatic system to the liver, where they are again hydrolyzed and re-esterified for storage. Prior to mobilization from the liver, the retinyl esters are hydrolyzed, and free retinol is complexed with the retinol-binding protein for secretion from the liver [101]. Different esterases are involved in this sequence. Hydrolysis of dietary retinyl esters in the lumen is catalyzed by pancreatic sterol esterase (steryl-ester acylhydrolase, cholesterol esterase, EC 3.1.1.13) [102], A bile salt independent retinyl-palmitate esterase (EC 3.1.1.21) located in the liver cell plasma hydrolyzes retinyl esters delivered to the liver by chylomicrons. Another neutral retinyl ester hydrolase has been found in the nuclear and cytosolic fractions of liver homogenates. This enzyme is stimulated by bile salts and has properties nearly identical to those observed for... 

The intestinal absorption of dietary cholesterol esters occurs only after hydrolysis by sterol esterase steryl-ester acylhydrolase (cholesterol esterase, EC 3.1.1.13) in the presence of taurocholate [113][114], This enzyme is synthesized and secreted by the pancreas. The free cholesterol so produced then diffuses through the lumen to the plasma membrane of the intestinal epithelial cells, where it is re-esterified. The resulting cholesterol esters are then transported into the intestinal lymph [115]. The mechanism of cholesterol reesterification remained unclear until it was shown that cholesterol esterase EC 3.1.1.13 has both bile-salt-independent and bile-salt-dependent cholesterol ester synthetic activities, and that it may catalyze the net synthesis of cholesterol esters under physiological conditions [116-118], It seems that cholesterol esterase can switch between hydrolytic and synthetic activities, controlled by the bile salt and/or proton concentration in the enzyme s microenvironment. Cholesterol esterase is also found in other tissues, e.g., in the liver and testis [119][120], The enzyme is able to catalyze the hydrolysis of acylglycerols and phospholipids at the micellar interface, but also to act as a cholesterol transfer protein in phospholipid vesicles independently of esterase activity [121],... 

Various pancreatic enzymes hydrolyze lipids, including lipase with its auxiliary protein colipase (see p. 270), phospholipase A2, and sterol esterase. Bile salts activate the lipidcleaving enzymes through micelle formation (see below). 

Cholesterol esterase hydrolyses sterol esters. Cholesterol is absorbed as free sterol (39), and the effects of phytostanol esters and phytosterol esters are mediated by the free phytostanol/sterol. 

Cholc.sterol esterase Acelylcholine.stera.se Corhoxypeptidase Cholinesterase... 

Sterol esterase activity is located in the cell membrane of white mustard Sinapsis alba) seedlings esters of Ci4 C,8 fatty acids are most rapidly attacked [13]. 

Several sources of cellular cholesterol contribute to RCT. Part of the process of RCT reflects peripheral (extra-hepatic) cholesterol synthesis. Despite the down-regulation of cholesterol synthesis mediated by the LDL receptor via the delivery of LDL, a considerable amount of sterol is made in peripheral tissues. The importance of this source of cholesterol to homeostasis may be as great as that of dietary cholesterol in many individuals. After hydrolysis of LDL-CE by cellular cholesterol esterases, this cholesterol is made available for recycling to the cell surface and can be recovered there by apo A1 for incorporation into HDLs. Cholesterol is also available from VLDLs, LDLs, and chylomicrons directly internalized by peripheral cells. Cholesterol from HDLs bypasses the lysosomal pathway and becomes part of recycling endosomes that return to the cell surface. Some of the cholesterol recovered on HDLs originates from blood cells. Finally, some cholesterol is transferred directly to other lipoproteins from chylomicrons, VLDLs, and LDLs, without entering the cell. 

Methods have been published that allow the classification of two types of esterases, the carboxylic ester hydrolases (CEHs) and the phosphoric triester hydrolases (PTEHs) (Anspaugh and Roe, 2004). The CEHs contain the B-esterases, which are inhibited by organophosphates. B-esierases include many other esterases, such as CarbE, acetylcholinesterase (AChE), cholinesterases (ChE), aryleslerases, sterol esterases, insect juvenile hormone esterases, aixl others. The determination of A-esterases uses a protocol for the detection of PTEHs. The PTEH assay allows for the identification of two subclasses of esterases, the A-esterase (known as aiyldialkylphos-phatase) and ditsopropyl fluorophosphatase. Both these enzymes metabolize OP compounds. 

Cholesterol esterase - Sterol-ester hydrolase 3.1.1.13 Pancreas and small intestine Cholesterol esters... 

Cholesterol esterase (CEase) plays important roles in the hydrolysis of sterol esters. This enzyme has stimulated research interest as a target in atherosclerosis and for the development of hypocholesterolemic agents since the 1990s. Peng and coworkers developed the synthesis ofphosphaisocoumarins and investigated these compounds as potential inhibitors of pancreatic cholesterol esterase (CEase) (10EJMC1955). 

A carboxylesterase (EC 3.1.1.1) from T. fusca [8, 86] and a steryl esterase (EC 3.1.1.13) from Melanocarpus albomyces [59] have also shown activity with PET oligomers and fabrics. The enzyme from M. albomyces with high specificity for fatty acid esters of sterols increased the hydrophilicity of PET fabrics. The highly hydrophobic serine hydrolase from T. fusca with a catalytic triad composed of serine, glutamic acid, and histidine hydrolyzed CTR and PET nanoparticles. The esterase showed high specificity towards short and middle chain-length fatty acyl esters of p-nitrophenol. In addition, p-nitrobenzyl esterases from Bacillus subtilis and B. licheniformis that hydrolyzed short chain dialkylphthalates and PET nanoparticles have been reported [74, 87]. 

Important reactions of free steroids include esterification, where esters and glycosides of steroid compounds are easily hydrolysed. These reactions in food raw materials are catalysed by sterol esterases and glycosidases, respectively. Other important reactions of steroids include elimination and substitution reactions and oxidation. Hydrogenation of steroids is of industrial importance. 

Finally it is clear that, unlike long-chain fatty acids which can appear in portal blood in limited amounts[32], cholesterol is absorbed exclusively into the lymphatic circulation[32,33]. A small amount of unesterified cholesterol can appear in lymph and is largely associated with chylomicron and lipoprotein "coat , or limiting membrane. However, this coat has a limited capability for significant transport, and the mass transport cholesterol (like that of triglycerides) requires esterification and incorporation into the lipoprotein core. Thus, the transfer of significant amounts of cholesterol from intestinal lumen to l3onph is associated with extensive esterification (70-90%) with fatty acids, and this occurs in the mucosal epithelial cells[11]. There are two intestinal enzymes potentially important in the esterification of unesterified cholesterol cholesterol esterase, or sterol ester hydrolase (EC. 

Of the two potentially esterifying enzymes associated with intestinal mucosa, sterol ester hydrolase, also referred to as cholesterol esterase (CE ase) has been extensively investigated in... 

The luminal requirements for bile salts are general, and do not adequately describe the known specifity for cholate and its conjugates which has been demonstrated in several species including man. This specifity appears to be a function, at least in part, of a cholic acid - dependent enzyme, sterol ester hydrolase (cholesterol esterase). 

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