Sterols steryl esters

Note Silica gel, kieselguhr and polyamide layers can be used as stationary phases. Not all acids are stained on RP layers. Amino layers yield a pale blue background. The detection limits are in the pg range for carboxylic acids [1], thioglycolic and dithioglycolic acids [2] and for antithyroid pharmaceuticals [4] they are about 5 ng per chromatogram zone for sterols and steryl esters [6]. 

Although not very commonly used in the separation of nentral hpids, two-dimensional systems have been nsed to separate hydrocarbons, steryl esters, methyl esters, and mixed glycerides that move close to each other in one-dimensional systems. Complex neutral lipids of Biomphalaria glabrata have been first developed in hexane diethyl ether (80 20), dried, and the plates have been turned 90°, followed by the second development in hexane diethyl ether methanol (70 20 10) for complete separation of sterol and wax esters, triglycerides, free fatty acids, sterols, and monoglycerides [54]. 

Sterols are minor constituents of most fats. Those of animal origin contain cholesterol and traces of other sterols, whereas plants contain phytosterols, of which p-sitosterol is the most common. Sterols occur in the free form or, after esterification to fatty acids through the 3-OH group, as steryl esters. The presence of sterols in archaeological residues can be a useful indicator of a plant or animal origin or an indicator of both if cholesterol and phytosterols are detected in the same sample. That noted, cholesterol is a potential contaminant of all archaeological samples subjected to handling. 

Saturated hydrocarbons Unsaturated hydrocarbons Wax esters Steryl esters Long chain aldehydes Triacylglycerols Long chain alcohols Free fatty acids Quinones Sterols... 

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],... 

Abidi, S. L. (2004). Capillary electrochromatography of sterols and related steryl esters derived from vegetable oils. J. Chromatogr. A 1059, 199—208. 

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. 

Figure D1.6.6 latroscan TLC-FID chromatograms of (A) a lipid fraction enriched with neutral lipids isolated from cod flesh and stored in ice (B) neutral lipids spiked with authentic 1 -0-palmityl-glyceryl ether dipalmitate (GE), coinciding in position with authentic highly unsaturated acids such as 22 6n-3 (C) hydrogenated neutral lipids spiked with GE. The solvent system was 97 3 1 (v/v/v) hexane/diethyl ether/formic acid for 40 min. Abbreviations O, origin SF, solvent front FFA, free fatty acid PL, phospholipids SE, steryl ester ST, free sterol TG, triglyceride. Reproduced from Ohshima et al. (1987) with permission from AOCS Press.

The important role of sterol components in the acquisition of freezing tolerance has recently been demonstrated using an Arabidopsis mutant with altered steryl-ester metabolism. Compared with the wild-type the mutant has no visible phenotype at standard growth temperature but exhibits clear symptoms when exposed to low temperatures (Hugly et al.,... 

Sitosterol and stigmasterol were the major components of celery seed oil. The other components were cholesterol, brassicasterol, campesterol, 97-campesterol, 95-avenasterol, 97-stigmasterol and 9 7-avenasterol (Zlatanov and Ivanov, 1995). Oil bodies isolated from celery cell suspension cultures contained at least 60% of the total steryl ester present in the cells. Free sterols comprised < 0.5% of the total lipid in the oil body. Sterylesters constituted 4.5% of the total lipid of celery oil bodies. The proportion of precursor 4-methylsterols in the free sterol fraction of celery was greater in the oil body (Dyas... 

Kamm el al. (2001) analysed intact steryl esters in the presence of silylated sterols by online transfer from HPLC to a 15 m low-polarity high temperature GC column. Steryl esters were quantified against a cholesteryl laurate internal standard and identified by offline thin layer chromatography-gas chromatography-mass spectrometry. When esters of sitosterol, stigmasterol and campesterol with the major cocoa butter acids were measured in cocoa butters from South America, Asia and Africa, no differences were apparent between cocoa butters of different geographical origin, or between deodorized and non-deodorized butters. 

No comprehensive comparison has been made of the proportions of the free and esterified sterols in cocoa butter with those of fats likely to be used in cocoa butter adulteration. However Gordon and Griffiths (1992) examined the sterol esters of palm kernel oil by isolation with TLC followed by GC and HPLC. They pointed out the problem of co-elution of triacylglycerols with steryl esters with GC. The characterization of esters of triterpene alcohols in CBA fats might well prove useful where the use of fats containing shea is suspected. 

Standard methods of analysis of total sterol content of oils involve saponification of the oil, followed by extraction and isolation of total sterols from the unsaponihable fraction by thin layer chromatography (TLC) (AOCS, 1998). Quantification of individual sterols involves silylation of the sterol fraction and analysis by gas chromatography (GC). Sterols and steryl esters in oils and fats can be analysed by LC-GC after silylation or acylation of the free sterols (Artho et al., 1993). An alternative approach to the analysis of intact steryl esters involves separation of sterols and steryl esters by solid phase... 

Figure 2.10. Lipase-catalyzed reaction on a mixture of FAStE and water in the presence or in the absence of MeOH. A, Hydrolysis of FA steryl ester and esterification of sterol with FFA. B, Lipase-catalyzed reactions in a mixture of FAStE, water and MeOH.

Shimada, Y., Nagao, T., Watanabe, Y., Takagi, Y., and Sugihara, A. 2003a. Enzymatic conversion of steryl esters to free sterols. /. Am. Oil Chem. Soc., 80,243-247. 

Keywords Plant sterol phytosterol sterol conjugate steryl ferulate gamma-oryzanol steryl glycoside acylated steryl glycoside steryl ester free sterol. 

Sterol acyltransferase (SGTase) and steryl ester hydrolase (SEHase)... 

Unesterified sterols modulate the function of eukaryotic membranes. In human cells, sterol is esterified to a storage form by acyl-co-enz)me A (CoA) cholesterol acyltransferase (SGTase). In plants, free sterols are associated mainly with microsomal membranes, whereas the steryl esters are stored in lipid granules. The esterification process may, thus, allow regulation of the... 

Bouvier-Nave, R and Benveniste, P. (1995) Sterol acyl transferase and steryl ester hydrolase activities in a tobacco mutant which overproduces sterols. Plant Sci, 110, 11-9. 

The preparation of high-purity tocopherols and phytosterols involves steps such as molecular distillation, adduct formation, liquid-liquid extraction, supercritical fluid extraction, saponification, and chromatography (175). The extraction of tocopherols from soybean oil deodorizer distillate by urea inclusion and saponification of free fatty acids resulted in good recovery of tocopherols (208). To improve the separation of sterols and tocopherols, Shimada et al. (209) used a lipase to esterify sterols with free fatty acids. Then the steryl esters and tocopherols were separated better by molecular distillation. Chang et al. (210) used supercritical fluid CO2 extraction to recover tocopherols and sterols from soybean oil deodorizer distillate. A patent by Sumner et al. (211) advocated treatment of the distillate with methanol to converted free fatty acids and other fatty acid esters to methyl esters that can then be removed by a stripping operation. Then separation of sterols and tocopherols could be carried out by molecular distillation. 

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