Esterases cholesterol esterase

Hydrolytic degradation can be assessed as noted above. Keep in mind, however, that in vivo hydrolytic attack is often accelerated or catalyzed by enzymes, local pH, and/or physiologic ions. Immersion in solutions containing an esterase, cholesterol esterase, and a protease has been shown to accelerate hydrolysis in vitro [34,35]. 

Page 1093 (Figure 26 9c) is adapted from crystallographic coordinates deposited with the Protein Data Bank PDB ID ICLE Ghosh D Wawrzak Z Pletnev V Z Li N Kaiser R Pangbom W Jornvall H Erman M Duax W L Structure of Un complexed and Linoleate Bound Candida Cholesterol Esterase To be published... 

Free cholesterol can also be determined, if cholesterol esterase is omitted. 

Parameter Cholesterol oxidase (CO) Cholesterol esterase (CE) Glucose oxidase (GOD) Peroxidase (POD)... 

One limitation of enzyme replacement therapy is the targeting of enzyme proteins to appropriate sites of substrate accumulation. Administration of a cholesterol esterase conjugated to albumin results in the degradation of pathologic cholesterol ester accumulations within the lysosomes of fibroblasts from a patient with cholesterol ester storage disease (246). 

Cholesterol Cholesterol esterase and cholesterol oxidase Medical care... 

A.L. Crumbliss, J.Z. Stonehuerner, R.W. Henkens, J. Zhao, and J.P. O Daly, A carrageenan hydrogel stabilized colloidal gold multi-enzyme biosensor electrode utilizing immobilized horseradish peroxidase and cholesterol oxidase/cholesterol esterase to detect cholesterol in serum and whole blood. Biosens. Bioelectron. 8, 331-337 (1993). 

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],... 

J. Hyun, C. R. Treadwell, G. V. Vahouny, Pancreatic Juice Cholesterol Esterase. Studies on Molecular Weigth and Bile Salt-Induced Polymerization , Arch. Biochem. Bio-phys. 1972, 752, 233-242. 

R. M. Stroud, Structure of Bovine Pancreatic Cholesterol Esterase at 1.6 A Novel Structural Features Involved in Lipase Activation , Biochemistry 1998, 37, 5107-5117. 

L. L. Gallo, S. B. Clark, S. Myers, G. V. Vahouny, Cholesterol Absorption in Rat Intestine Role of Cholesterol Esterase and Acyl Coenzyme A Cholesterol Acyltransferase , J. Lipid Res. 1984, 25, 604-612. 

E. M. Kyger, D. J. S. Riley, C. A. Spilburg, L. G. Lange, Pancreatic Cholesterol Esterases. 3. Kinetic Characterization of Cholesterol Ester Resynthesis by Pancreatic Cholesterol Esterases , Biochemistry 1990, 29, 3853-3858. 

There are a few reported cases of esterases that catalyze not only hydrolysis but also the reverse reaction of ester formation, in analogy with the global reaction described for serine peptidases (Fig. 3.4). Thus, cholesterol esterase can catalyze the esterification of oleic acid with cholesterol and, more importantly in our context, that of fatty acids with haloethanols [54], Esterification and transesterification reactions are also mediated by carboxyleste-rases, as discussed in greater detail in Sect. 7.4. 

J. A. Doom, T. T. Talley, C. M. Thompson, R. J. Richardson, Probing the Active Site of Butyrylchohnesterase and Cholesterol Esterase with Isomalathion Conserved Stereoselective Inactivation of Serine Hydrolases Structurally Related to Acetylchohnesterase , Chem. Res. Toxicol. 2001, 14, 807-813. 

Fig. 7.4. A simple topographical model showing the absolute configuration of the acetates reacting faster with cholesterol esterase and lipase (modified from [19]). S = smaller group ...

Thioesters play a paramount biochemical role in the metabolism of fatty acids and lipids. Indeed, fatty acyl-coenzyme A thioesters are pivotal in fatty acid anabolism and catabolism, in protein acylation, and in the synthesis of triacylglycerols, phospholipids and cholesterol esters [145], It is in these reactions that the peculiar reactivity of thioesters is of such significance. Many hydrolases, and mainly mitochondrial thiolester hydrolases (EC 3.1.2), are able to cleave thioesters. In addition, cholinesterases and carboxylesterases show some activity, but this is not a constant property of these enzymes since, for example, carboxylesterases from human monocytes were found to be inactive toward some endogenous thioesters [35] [146], In contrast, allococaine benzoyl thioester was found to be a good substrate of pig liver esterase, human and mouse butyrylcholinesterase, and mouse acetylcholinesterase [147],... 

R. J. Kazlauskas, A. N. E. Weissfloch, A. T. Rappaport, L. A. Cuccia, A Rule to Predict Which Enantiomer of a Secondary Alcohol Reacts Faster in Reactions Catalyzed by Cholesterol Esterase, Lipase from Pseudomonas cepacia, and Lipase From Candida rugosa, J. Org. Chem. 1991, 56, 2655 - 2665. 

L. D. Sutton, J. S. Stout, D. M. Quinn, Dependence of Transition-State Structure on Acyl Chain Length for Cholesterol Esterase Catalyzed Hydrolysis of Lipid p-Nitrophen-yl Esters ,./. Am. Chem. Soc. 1990, 112, 8398-8403. 

All of the above examples are acetates of active alcohols. Here, we also mention the acetate of a phenol, namely the provitamin a-tocopheryl acetate, whose natural enantiomer of absolute configuration (2R,47 ,87 ) is shown as 8.73. a-Tocopheryl acetate is a substrate of cholesterol esterase (EC 3.1.1.13), and was hydrolyzed in rats faster than its (2S,47 ,87 )-epimer. In vitro experiments required a-tocopheryl acetate to be dispersed as a micellar pseudosolution, and the nature of the bile salt used to prepare micelles had a profound effect on the substrate stereoselectivity of the reaction [95] [96], Only when the micelle composition approximated that of the gastrointestinal tract did the in vitro substrate stereoselectivity resemble that seen in vivo. 

A. N. J. Moore, P. J. Dutton, H. A. Zahalka, G. W. Burton, K. U. Ingold, Bile Salt Modulated Stereoselection in the Cholesterol Esterase-Catalyzed Hydrolysis of alpha-To-copheryl Acetates ,./. Am. Chem. Soc. 1995, 117, 5677-5686. 

Figure 8. Enzymatic preparation of (S)- and (R)-furyl methyl carbinol. TADH, Thermoanaerobium brokii alcohol dehydrogenase (NADPH was regenerated by glucose/glucose dehydrogenase from Bacillus cereus obtained from Amano.) CCL, lipase from Candida cvlindraceae ChE, cholesterol esterase from Pseudomonas.

In a like manner, a co-polymer of styrene and acryloxysuccinimide with a 10 to 1 ratio was prepared. Enzymes immobilized on this type of polymer had different physical properties. They are soluble in organic solvents such as dioxane and DMF, but insoluble in aqueous solutions. Lipases and cholesterol esterase immobilized on this type of polymer are very stable and active in several organic solvents, and have been used in several enantioselective transformations. The protocols for the immobilization are depicted in Figure 13. 

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. 

Intestinal esterase activity. Oil was administered to rats at different doses with or without clofibrate for 15 days. The hypolipidemic action of clofibrate was not influenced by the amount of fat. Clofibrate did not affect lower cholesterol concentration... 

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