Esterification lecithin

Rgure 5 The effect of apo-CRBP(l) on the rates of retinol esterification (lecithin retinol acyltransferase (LRAT)) and retinyl ester hydrolysis (REH). 

Simon, J. B., and Scheig, R., Serum cholesterol esterification in liver disease. Importance of lecithin-cholesterol acyltransferase. New Engl. J. Med. 283,841-846 (1970). 

Naoe et al. [239] used the sugar ester DK-F-110, a mixture of sucrose esters of fatty acids, as a nonionic surfactant along with isopropyl alcohol and hexane in a reverse micellar system to extract cytochrome C. This surfactant has a critical micellar concentration of 0.5 g/1 and HLB of 11. Aqueous phase pH was found to have a major role in the forward extraction and optimum extraction was achieved at pH 8.0. However, for optimum back extraction, addition of isopropyl alcohol at 20 vol.% was found to be very essential. Further, the esterification reaction rate of Rhizopus delemar lipase was found to be maximum in DK-F-110 systems and also higher than those obtained in AOT and lecithin-RMs at a water concentration of 0.25 mol l h... 

Retinol (vitamin A) is found in foods of mammalian origin in the form of retinyl ester, or in fruits and vegetables as carotenoids with provitamin A activity, especially P-carotene (provitamin A). In enterocytes, retinol binds to cellular retinol-binding protein type II (CRBPII), which directs the esterification by the enzyme lecithin retinol acyltransferase (LRAT). 

Esterification of cholesterol When cholesterol is taken up by HDL, it is immediately esterified by the plasma enzyme phos-phatidylcholine cholesterol acyltransferase (PCAT, also known as LCAT, in which "L" stands for lecithin). This enzyme is synthesized by the liver. PCAT binds to nascent HDLs, and is activated by apo A-l. PCAT transfers the fatty acid from carbon 2 of phosphatidyl-... 

The metabolism of HDL probably involves interaction with both hepatic and peripheral cells, as well as with other lipoproteins. HDL may remove cholesterol from tissues, the "scavenger hypothesis (11,12). The cholesterol may then be esterifed by the action of lecithin cholesterol acyl transferase. HDL may provide cholesterol to the liver for bile acid synthesis (13) and some HDL may be catabolized by the liver in the process. HDL has not been found to interfere with the binding of LDL in cultured human fibroblasts (6). However, in cultured human arterial cells, porcine or rat hepatocytes, and rat adrenal gland, there appears to be some competition of HDL with LDL binding sites, suggesting the presence of a "lipoprotein-binding" site (14). 

Many food colloids are stabilized from proteins from milk or eggs [817]. Milk and cream, for example, are stabilized by milk proteins, such as casein micelles, which form a membrane around the oil (fat) droplets [817]. Mayonnaise, hollandaise, and bearnaise, for example, are O/W emulsions mainly stabilized by egg-yolk protein, which is a mixture of lipids (including lecithin), proteins, and lipoproteins [811,817]. The protein-covered oil (fat) droplets are stabilized by a combination of electrostatic and steric stabilization [817]. Alcohols may also be added, such as glycerol, propylene glycol, sorbitol, or sucrose sometimes these are modified by esterification or by... 

T7. Thanabalasingham, S., Thompson, G. R., Trayner, T. I., Myant, N. B., and Soutar, A. K., Effect of lipoprotein concentration and lecithin cholesterol acyltransferase activity on cholesterol esterification in human plasma after plasma exchange. Eur. J. Clin. Invest. 10, 45-48 (1980). 

Native or hydrogenated palm, palm kernel, rapeseed, soya, pemiut, coconut, castor, cotton oils, cocoa butter and their derivatives (obtained by fractionation, esterification, concentration mid/or reconstitution fatty acids mid cohols, mono-, di- and triglycerides, cocoa butter substitutes, mmgmine, shortenings, acetylated glycerides, lecithins, etc)... 

Retinaldehyde, when bound to retinol binding protein II (CRBPII), serves as a substrate for retinal reductase resulting in the production of retinol (14), which then binds to cellular retinol binding protein (CRBP) forming holo-CRBP. Holo-CRBP seems to be the preferred substrate for an esterification reaction (Fig. 7.6) mediated by lecithin retinol acyl transferase (LRAT), a microsomal enzyme that uses acyl groups donated from phosphatidylcholine (14).In cells not expressing CRBP, retinol esterification is carried out by a different enzyme, acyl CoArretinol acyl transferase (ARAT). 

The ll-palm-A -THC can be hydrolyzed to II-OH-A -thc by cholesterol esterase and triacylglycerol lipase but not by phospholipase A, acetylesterase or phosphotransacetylase (16). An attempt to modify the retention of fatty acid-conjugated DDT metabolites was carried out by injecting the DDT-treated rats with sodium salt of various bile acids, heparin or lecithin of which all were known to affect the esterification or ester hydrolysis by the cholesterol esterase system. The results Indicated a significant decrease in the retention of the conjugated DDT metabolites in the rat liver and spleen (17). 

Phosphatidylcholines are the most important fraction of soybean lecithin. Then-content may be increased by transesterihcation with choline hydrochloride, catalyzed by phospholipase D. Phosphatidylcholine content may thus be increased from 30% up to 60 or 70%, or from 75 or 80% to more than 90% (Juneja et ah, 1989). Similarly, phosphatidylserine can be produced from phosphatidylcholine by enzyme-catalyzed inter-esterification (Yaqoob et al., 2001). Another modification of lecithins is the inter-esterihcation of lysophosphatidylcholine with fish PUFA under catalytic action of phospholipase A2 (Na et al., 1990). 

The esterification of cholesterol in animals has attracted considerable research because of the possible involvement of cholesterol and its ester in various disease states (cf. Glomset and Norum, 1973, and Sections 12.1, 12.3 and 12.6). Cholesterol esters are formed by the action of lecithin cholesterol acyltransferase (LCAT, EC 2.3.1.43) which is particularly active in plasma (cf. Sabine, 1977, for a review of cholesterol metabolism). The reaction involves transfer of a fatty acid from position 2 of lecithin (phosphatidylcholine) to the 3-hydroxyl group of cholesterol with the formation of monoacyl-phosphatidylcholine. Although LCAT esterifies plasma cholesterol solely at the interface of high-density lipoprotein and very-low-density lipoprotein, the cholesterol esters are transferred to other lipoproteins by a particular transport protein (CETP cholesteryl ester transfer protein). Cholesteryl esters, in contrast to free cholesterol, are taken up by cells mostly via specific receptor pathways (Brown et aL, 1981), are hydrolysed by lysosomal enzymes and eventually re-esterified and stored within cells. LCAT may also participate in the movement of cholesterol out of cells by esterifying excess cholesterol in the intravascular circulation (cf. Marcel, 1982). 

Lipases from Rhizomucor miehei and Candida antarclica are immobilised in lecithin microemulsion based gels formed with agar and hydroxypropylmethyl cellulose. It is found that both lipases keep their catalytic function after their entrapment in the gels, catalysing the esterification reaction of 1-propanol with fatty acids in non-polar hydrocarbons at room temperature. Various parameters, which affect the lipase catalytic behaviour such as the nature and the concentration of geUing agent, as well as the concentration of alcohol, are examined. 

Fig. 4. Esterification of cholesterol catalyzed by lecithin-cholesterol acyltransferase (LCAT).

One interesting property of FED plasma is its poor capacity to activate cholesterol esterification [6]. Specifically it will not activate the formation of cholesterol esters in HDL, but it will do so in other lipoproteins. FED plasma lacks, therefore, a-HDL lecithin cholesterol acyltransferase (LCAT), although p-LCAT is present in normal amounts. 

R. delemar AOT, Lecithin C12E4 Esterification of aliphatic alcohols, glycerol and ethylene glycol by fatty acids [42,45,111,11 ... 

P. cepacia AOT Lecithin Esterification of various aliphatic alcohols and glycerol by fatty adds [46,48]... 

Nagayama, K., Matsura, S., Doi, T., Imai, M. 1998. Kinetic characterization of esterification catalyzed by Rhizopus delemar lipase in lecithin-AOT microemulsion systems. J. Mol. Catal. B Enzym. 4, 25-32. 

Monoacylglycerols and diacylglycerok can ako be esterified using phosphorus pentoxide. For example, esterification of 1,2-diacyl-sn-glycerol yields phosphatidic (1,2-diacyl-sn-glycerol 3-phosphate) and the corresponding bisphosphatidic acid and their positional isomers. Both acids are natural-identical products, which serve as substitutes for lecithin. Ammonium phosphatides (E442) are approved in the EU as emulsifiers. 

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