Phosphatidyl ethanolamines, structure

Figure 9.18 Idealized structures of hydrated didodecyl-phosphatidyl ethanolamine showing some typical bicontinuous cubic phases. (Adapted from Seddon et al, 1990 see this reference for the indicated crystallographic nomenclature.)...

Many single-chain amphiphiles form cubic phases when added to water in a given composition. Two of the most well known are didodecyl-phosphatidyl ethanolamine, and mono-olein. Figure 9.18 shows some idealized bicontinous cubic structures of the former, including typical inverse ones. This is also highly viscous and optically transparent as are most of the other cubic phases. 

Dairy phospholipids are important structurally, because they are able to stabilise emulsions and foams, and to form micelles and membranes (Jensen and Newburg, 1995). Phospholipids also have the potential to be pro-oxidants, because they contain mono-unsaturated and poly-unsaturated fatty acids and have the ability to attract metal ions. Phosphatidyl ethanolamine binds copper strongly and is believed to be important in copper-induced oxidation in milk (O Connor and O Brien 1995 Deeth, 1997). The polyunsaturated fatty acids and metal ions accelerate lipid oxidation, especially when heat is applied hence, phospholipids can be degraded during the processing of milk. However, in dairy products, the situation is complex and it appears that phospholipids are able to act as either pro-oxidants or antioxidants, depending on the pH, ratio of water and phospholipid species (Chen and Nawar, 1991). 

The structural formulas of phosphatidyl choline and the other principal phosphoglycerides—namely, phosphatidyl ethanolamine, phosphatidyl serine, phosphatidyl inositol, and diphosphatidyl glycerol—are given in Figure 12.5. 

Fig. 3. Molecular models for the conversion of di-DHA phosphatidyl ethanolamine or di-DPA (n-6) phosphatidylethanolamine (PE) into phosphatidylserine (PS) by base exchange catalyzed by PS synthase. Molecular models were computed by energy minimization of the phospholipid structure given the di-DHA PE structure.

From work with beef-heart mitochondrial cristae and Naja Naja siamensis phospholipase A it is known that phosphatides are digested in the order phosphatidyl-ethanolamine, phosphatidylcholine and diphosphatidylglycerol (cardiolipin). The majority of the lysophosphatides seems to stay in the membrane. Low level digestion with phospholipase A, sufficient to cause almost complete breakdown of phosphatidyl-ethanolamine and phosphatidylcholine does not produce noticeable changes in membrane structure. Another Naja Naja phospholipase A preparation was also shown to attack phosphatidylethanolamine faster than phosphatidylcholine (Gallai-Hatchard and Gray, 1968)... 

Recently, the competitive adsorption dynamics of phospholipid/protein mixed system at the chloroform/water interface was investigated by using the drop volume technique. The three proteins P-Lactoglobulin, P-Casein, and Human Serum Albumin were used in this study. To investigate the influence of the phospholipid structure at concentrations close to the CAC (critic aggregation concentration) the four lipids dipalmitoyl phosphatidyl choline (DPPC), dimyristoyl phosphatidyl choline (DMPC), dimyristoyl phosphatidyl ethanolamine (DMPE)... 

Recall What structural features do a triacylglycerol and a phosphatidyl ethanolamine have in common How do the structures of these two types of lipids differ ... 

Structural Analysis of Phosphatidylcholine (PC) Fraction and Phosphatidyl-ethanolamine (PE) Fraction in Yolk Depending on Dietary Fat (7% fish oil)... 

Chapman and Morrison (1966) have found NMR evidence favoring a dipolar ionic form for the phosphatidyl ethanolamines. Also, their infrared spectra of chloroform solutions favor a dipolar ionic structure. The evidence was as follows if dioleoyl-phosphatidyl ethanolamines exist in chloroform in a nonionic form, then intense bands in the 3300 cm region should occur because of NH stretching frequencies. Bands were found at 3058, 2710, 2538, and a probable band at 3021 cm , which they correlated with vibrations of an NHj group. A comparison of the spectra of dioleoyl-phosphatidyl ethanolamine and a dipolar ionic amino acid, such as alanine, showed almost identical spectra in the 4000 to 2000 cm region. The spectrum of the non-ionized compound, OL-a-alanine methyl ester in chloroform shows intense absorption in the 3300 cm region characteristic of a free primary amino group. 

Abrahamsson etal. (1978) have described two hydrid subcells in complex lipids. Thus a twinned version of the O i subcell, with dimensions a = 10.3 A, 6 = 7.5 A, c = 2.54 A, was observed in the crystal structure of a cholesteryl ester (Abrahamsson and Dahlen, 1977), in 1,2-dilauroyl-DL-phosphatidyl-ethanolamine (Hitchcock et al., 1974) and also in the corresponding dipalmitoyl analogue (Dorset, 1976). 

FIGURE 49.7 (A) Structural elucidation of lipids by MALDI-TOF/TOF analysis (B) analysis of the MS/MS spectrum of lyso-phosphatidylcholin several fragments were assigned to lipid moeities (marked in the lipid structure representation). Intens. [a.u.], intensity (in arbitrary units) PG, phosphatidyl glycerol PE, phosphatidyl ethanolamin PA, phosphatidic acid PC, phosphatidyl cholin SM, sphingomyelin LPC, lyso-phosphatidyl cholin. 

In nature, the more common amphiphiles are phospholipids. These are derivatives of glycerol (1,2,3-trihydroxypropane), in which two alcohols form esters with long chain carboxylic acids. The third alcohol forms a phosphate ester, and the phosphate then makes another ester with a simpler alcohol. This creates structures such as phosphatidyl choline, phosphatidyl serine, and phosphatidyl ethanolamine (see next page). The polar group can... 

Figure 6 Artist s view of lipid/protein interaction derived from the electron density model from XR measurements and available structural data. The lipid monolayer is dipalmitoyl phosphatidyl ethanolamine (DPPE) and the protein is a membrane surface layer protein from B. sphaericus (from ref. [28]). The structural model sketched was based [28, 29] on the electron density profile (black line) inverted from measured reflectivity data as described in the text.

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