Lysolecithines

Hauser, H. (1987). Spontaneous vesiculation of uncharged phospholipid dispersions consisting of lecithin and lysolecithin, Chem. 

Kitagawa, T., Inoue, K., and Nojima, S. (1976). Properties of lip-somal membranes containing lysolecithin, J. Biochem. (Tokyo). 

Lysolecithin (lysophosphatidylcholine) may be formed by an alternative route that involves lecithin cholesterol acyltransferase (LCAT). This enzyme. 

Familial lecithimcholesterol acyltransferase (LCAT) deficiency Absence of LCAT leads to block in reverse cholesterol transport. HDL remains as nascent disks incapable of taking up and esterifying cholesterol. Plasma concentrations of cholesteryl esters and lysolecithin are low. Present is an abnormal LDL fraction, lipoprotein X, found also in patients with cholestasis. VLDL is abnormal ( 3-VLDL). 

Kugiyama K, Kerns SA, Morrisett JD, Roberts R, Henry PD (1990) Impairment of endothelium-dependent arterial relaxation by lysolecithin in modified low-density lipoproteins. Nature 344 160-162... 

Acid glycerophosphatides Phosphatidyl ethanolamine Lecithin Sphingomyelin Lysolecithin... 

Lysolecithins act by dissolving cholesterol and cause massive losses of the sterol from membranes (19). Lysolecithins have been shown to cause the formation of openings 300-400 A in diameter in erythrocyte plasma membranes (20). Unlike saponins, lysolecithin membrane openings are permanent. 

The stain/fixation method is usually used for surface markers that can withstand fixation and is followed by the application of a DNA-binding fluoro-chrome. The fixation/stain method is used not only for surface markers that can withstand fixation, but also for intracellular constituents, such as cytoplasmic proteins, nuclear membrane, and nuclear proteins. This is accomplished by using a crosslinking fixative (e.g., paraformaldehyde [PFA] or formalin) followed by a permeabilizing agent (e.g., Triton X-100, Tween-20, saponin, or lysolecithin). Some of the precipitating agents (e.g., ethanol, methanol, or acetone) can also be used for permeabilization after the initial fixation with PFA or formalin, or they can be used alone for both fixation and permeabilization (see Chapter 8). 

Phospholipids are digested and absorbed in a similar manner to that of triacylglycerol. Pancreatic lipase has some hydrolytic activity towards phospholipids and removes the fatty acid from the 1-position. The product is a lysophospholipid such as lysolecithin (Figure 4.12). It also acts as a detergent and contributes to the stability of the mixed micelles. 

Figure 4.12 Hydrolysis of a phospholipid (lecithin) in the lumen by a phospholipase. Lysolecithin is a lysophospholipid and is a detergent. At high concentrations it can damage membranes. It is also produced during repair of damaged phospholipids (Chapter 11)...

This enzyme [EC 2.3.1.23], also called lysolecithin acyl-transferase and lysophosphatidylcholine acyltransferase, catalyzes the reaction of an acyl-CoA derivative with 1-acyl-5 n-glycero-3-phosphocholine to yield coenzyme A and l,2-diacyl-5 n-glycero-3-phosphocholine. The enzyme preferentially acts on unsaturated acyl-CoA derivatives, but l-acyl-5 n-glycero-3-phosphoinositol can also act as the acceptor. 

At their critical micelle concentrations, surface active agents (such as sodium dodecyl sulfate, Triton X-100, lysolecithin, and bile salts) self-associate into spherical or rod-shaped structures. Because dilution to below the c.m.c. results in rapid disassembly or dissolution of these detergent micelles, micelles are in dynamic equilibrium with other dissolved detergent molecules in the bulk solution. 

Portmann, M Landau, E. M., and Luisi, P. L. (1991). Spectroscopic and rheological studies of enzymes in rigid lipidic matrices the case of a-chymotrypsin in a lysolecithin/water cubic phase. J. Phys. Chem., 95, 8437 0. 

Kugimiya, M., Donovan, J. W. (1981). Calorimetric determination of the amylose-lysolecithin complex. Journal of Food Science, 46, 765. 

Forstermann, U., Goppelt-Strube, M., Frolich, J. C., and Busse, R. (1986). Inhibitors of acylcoenzyme A Lysolecithin acyltransferase activate the production of endothelium-derived vascular relaxing factor. J. Pharmacol. Exp. Ther. 238, 352-359. 

T6. The Action of Phospholipases The venom of the Eastern diamondback rattler and the Indian cobra contains phospholipase A2, which catalyzes the hydrolysis of fatty acids at the C-2 position of glycerophospholipids. The phospholipid breakdown product of this reaction is lysolecithin (lecithin is phosphatidylcholine). At high concentrations, this and other lysophospholipids act as detergents, dissolving the membranes of erythrocytes and lysing the cells. Extensive hemolysis may be life-threatening. 

Figure 4. High resolution proton magnetic resonance spectra of lysolecithin and membrane fragments dispersed with lysolecithin in Dg0 (4)...

Influence of Intermolecular Spacing on Enzymic Hydrolysis of Lecithin Monolayers. When snake venom phospholipase A is injected under a lecithin monolayer, it splits lecithin into lysolecithin and free fatty acid. The change in polar groups of the monolayer results in a change of surface potential. However, if prior to injection of enzyme into the subsolution, a lecithin monolayer is compressed to such a surface pressure that the active site of the enzyme is unable to penetrate the monolayer, hydrolysis does not proceed. For monolayers of dipalmitoyl, egg, soybean, and dioleoyl lecithins the threshold surface pressure values at which hydrolysis does not proceed are 20, 30, 37, and 45 dynes per cm., respectively (40). This is also the same order for area per molecule in their surface pressure-area curves, indicating that enzymic hydrolysis of lecithin monolayers is influenced by the unsaturation of the fatty acyl chains and hence the intermolecular spacing in monolayers (40). 

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