Lecithins formation

Esko, J.D., Wermuth, M.M., and Raetz, C.R., 1981, Thermolabile CDP-chohne synthetase in an animal ceh mutant defective in lecithin formation. J. Biol. Chem. 256 7388-7393 Esko, J.D., Nishijima, M., and Raetz, C.R., 1982, Animal cells dependent on exogenous phosphatidylchohne for membrane biogenesis. Proc. Natl. Acad. Sci. USA. 79 1698-1702 Exton, J. H., 1994, Phosphatidylchohne breakdown and signal transduction, Biochim. Biophys. Acta 1212 2642. 

CAS 62-49-7. (CH3)3N(OH)CH2CH2OH. Member of the vitamin B complex. Essential in the diet of rats, rabbits, chickens, and dogs. In humans it is required for lecithin formation and can replace methionine in the diet. There is no evidence of disease in humans caused by choline deficiency. It is a dietary factor important in furnishing free methyl groups for transmethylation has a lipotropic function. 

Lord JM, Kagawa T, Moore TS, Beevers H. E.R. as the site of lecithin formation in castor bean endosperm. J Cell Biology, 1973 57 659-667. 

The original pathway described for the biosynthesis of sphingomyelin is analogous to the reaction for lecithin formation (Scibney and Kennedy, 1958). 

Cationic surfactants may be used [94] and the effect of salinity and valence of electrolyte on charged systems has been investigated [95-98]. The phospholipid lecithin can also produce microemulsions when combined with an alcohol cosolvent [99]. Microemulsions formed with a double-tailed surfactant such as Aerosol OT (AOT) do not require a cosurfactant for stability (see, for instance. Refs. 100, 101). Morphological hysteresis has been observed in the inversion process and the formation of stable mixtures of microemulsion indicated [102]. 

In nutrition, the most important function of choline appears to be the formation of lecithin (phosphatidylcholine) (2) and other cb oline-containing pho sphohpids. 

The solubilization of water in lecithin-reversed micelles has been found to be an exothermic process. This finding confirms that water interacts with the zwitterionic head group of lecithin, promoting the formation of strong intermolecular H bonds [104]. 

The formation of a nucleosil bonded lecithin by means of an imidazolide is described in reference [141]. See also Chapter 4, page 165. 

Totally synthetic bilayers show liquid crystalline properties similar to those of lecithin bilayers (Nagamura et al., 1978 Kano et al., 1979). Bilayer formation has also been observed for dialkyl compounds with anionic head groups such as [2] and [3] (Kunitake and Okahata, 1978a Mortara et al., 1978), and with nonionic and zwitterionic head groups as in [4] and [5] (Okahata et al., 1978a). 

Studies of the reaction of ozone with simplified lipid systems have shown that malonaldehyde can be produced by direct ozonolysis. The use of malonaldehyde assay as an index of lipid peroxidation is therefore invalid in ozone studies. Liposomes formed from egg lecithin and prepared in aqueous media were quite resistant to ozone, but the contribution of polyconcentric spheres to this resistance has not been fully assessed. However, the bilayer configuration, with the susceptible unsaturated fatty acids shielded from ozone by the hydrophilic areas of the molecule, may be resistant. In hexane, where the fatty acid moieties are exposed, ozone reacts stoichiometrically with the double bonds. The experiments with aqueous suspensions of phosphatidylcholine gave no evidence of the formation of lipid peroxides,nor did experiments with films of fatty acids exposed to ozone. ... 

Many substances as found in nature (lipids) exhibit unique properties in aqueous media. Some lipids (such as lecithins or alike), when dispersed in water, form very well-defined assemblies, in which the alkyl part of the molecule is in close proximity to each other. This leads to self-assembly formation with many important consequences. 

NA Mazer, GB Benedeck, MC Carey. Quasielastic light-scattering studies of aqueous biliary lipid systems. Mixed micelles formation in bile salt-lecithin solutions. Biochemistry 19 601-615, 1980. 

In the bile cholesterol is kept soluble by fats, phospholipids like lecithin and by bile acids. The important bile acids in human bile are cholic acid, chen-odeoxycholic acid or chenodiol and ursodeoxycholic acid or ursodiol. Bile acids increase bile production. Dehydrocholic acid, a semisynthetic cholate is especially active in this respect. It stimulates the production of bile of low specific gravity and is therefore called a hydrocholeretic drug. Chenodiol and ursodiol but not cholic acid decrease the cholesterol content of bile by reducing cholesterol production and cholesterol secretion. Ursodiol also decreases cholesterol reabsorption. By these actions chenodiol and ursodiol are able to decrease the formation of cholesterolic gallstones and they can promote their dissolution. 

When mesophase, that is, liquid crystal, consisting of three components of bile salt, lecithin and cholesterol was produced, deposition of calcium salts of bile acids was observed on the cholesterol disk surface. The relation between mesophase formation and calcification will be elucidated in this paper. 

In general, GUDC is known to produce a mesophase during dissolution of cholesterol(CHL) in the presence of lecithin(EL) in vitro, eind then increases the dissolution rate of CHL ty the mesophase formation. However, the effect is less than that of GCDC in vivo. 

Figure 9.14 The simple addition of a minimal amount of water to a hydrocarbon solution of lecithin (or other phospholipids) brings about the formation of an organogel. (Adapted from Scartazzini and Luisi, 1988.)...

Lecithin. A mixt of the diglycerides of stearic, palmitic and oleic acids, linked to the choline ester of phosphoric acid. Yellowish-white, waxy mass, obtained either from eggyolk or soybeans. Insol in w sol in ale, chlf and eth. Lecithin was used in Composition C (RDX 88.3, nonexpl oily plasticizer 11.1 lecithin 0.6%) to help prevent the formation of large crysts of RDX which would increase the sensitivity of the compn (Refs 1 4)... 

The fourth major lipoprotein type, high-density lipoprotein (HDL), originates in the liver and small intestine as small, protein-rich particles that contain relatively little cholesterol and no cholesteryl esters (Fig. 21-40). HDLs contain apoA-I, apoC-I, apoC-II, and other apolipoproteins (Table 21-3), as well as the enzyme lecithin-cholesterol acyl transferase (LCAT), which catalyzes the formation of cholesteryl esters from lecithin (phosphatidylcholine) and cholesterol (Fig. 21-41). LCAT on the surface of nascent (newly forming) HDL particles converts the cholesterol and phosphatidylcholine of chylomicron and VLDL remnants to cholesteryl esters, which begin to form a core, transforming the disk-shaped nascent HDL to a mature, spherical HDL particle. This cholesterol-rich lipoprotein then returns to the liver, where the cholesterol is unloaded some of this cholesterol is converted to bile salts. 

Different factors govern the formation of these molecular compounds. Where lipids and related substances are concerned the governing factor is the realization of the best hydrophilic-lipophilic balance producing hydration or dispersion. The case of lecithin and sodium cholate associated in the presence of water may be used to illustrate the conditions of association and formation of different types of structure and of micelles. 

Discontinuities are seen in the relationship between increase in film pressure, An, and lipid composition following the injection of globulin under monolayers of lecithin-dihydro-ceramide lactoside and lecithin-cholesterol mixtures. The breaks occur at 80 mole % C 16-dihydrocaramide lactoside and 50 mole % cholesterol. Between 0 and 80 mole % lactoside and between 0 and 50 mole % cholesterol the mixed films behave as pure lecithin. Two possible explanations are the formation of complexes, having molar ratios of lecithin-lactoside 1 to 4 and lecithin-cholesterol 1 to 1 and/or the effect of monolayer configurations (surface micelles). In this model, lecithin is at the periphery of the surface micelle and shields the other lipid from interaction with globulin. 

The role of lecithin as an auxiliary lipid in the specific interaction of lactosides with globulin in monolayers is related to two processes complex formation between 3 or 4 molecules of lactoside and each lecithin molecule, and the protection of the lactoside molecules in surface micelles from nonspecific interaction. The location of lecithin at the periphery of the surface micelle would explain why the mixed micelle behaves as lecithin in nonspecific interaction. Lactoside molecules, located in the center of the surface micelle, would be in a position to interact specifically with antibody in the aqueous subphase (5). 

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