Cephalins methylation

Phosphatidyl ethanolamines —ch2ch2nh3 Large amounts in animals, plants and microorganisms Old trivial name is cephalin. Methyl and dimethyl ethanolamine derivatives also occur... 

Phosphatidylcholine can be synthesized by the pathway shown in Figure 14.3. Decarboxylation of phosphatidylserine to phosphatidylethanolamine (cephalin) is followed by methylation in which S-adenosylmethionine is the methyl donor to yield successively the relatively rare mono- and dimethyl derivatives, then phosphatidylcholine. 

PE (trivial name cephalin ) also has a net neutral charge (Fig. 1). PE is widespread and usually the second most abundant phospholipid in animal and plant membranes. It is also the main lipid component of microbial membranes. In animal tissues, phosphatidylethanolamine may exist in diacyl, aUcylacyl and alkenylacyl forms. Moreover, animal phosphatidylethanolamine usually contains higher levels of arachidonic and docosahex-aenoic acids in comparison with the other zwitterionic phospholipid, PC. The partly methylated derivatives of PE (phos-phatidyl-A -methyl-ethanolamine, phosphatidyl-Af -dimethyl-... 

Centura A Gelatin. See Gelatin Cenwax G. See Hydrogenated castor oil Cenwax ME. See Methyl hydroxystearate CEPA 2-CEPA. See Ethephon Cephalins... 

The fatty acid portions are usually palmityl, stearyl, or oleyl. The structure shown is a cephalin the three protons on the nitrogen are replaced by methyl groups in the lecithins. Both types of phospholipids are widely distributed in the body, especially in... 

Phosphonic acids are formed from phosphate esters by intramolecular rearrangement (Fig. 47). Ciliatin (2-aminoethylphosphonic acid) is a constituent of phosphonocephalin, which corresponds structurally to cephalin (D 3.2.4), and is incorporated into membranes. Ciliatin may also be methylated to the iV-trimethyl derivative, which corresponds to choline. 

The best known of the nitrogen constituents of the phosphatides are choline, found in lecithin (phosphatidyl choline) ethanolamine, in cephalin (phosphatidyl ethanolamine) and serine, in phosphatidyl serine. In recent years small amounts of phosphatides containing the partially methylated bases, methylaminoethanol and dimethylaminoethanol have been discovered in Neurospora (64) and in liver (56). The phosphatide bases are interrelated by the metabolic cycle shown in Fig. 2. The reactions concerned with the formation of ethanolamine and its methylation to choline are discussed in the following sections. 

The Cephalins differ from lecithins in their low solubility in alcohol. They con t of two main fractions, the ethanolamine cephalins and the serine cephalins. As is evident from the partial formulas, the base ethanolamine, HO—CH —CHj— NH2, or the amino acid serine, HO—CH —CH(COOH)—NH2, replaces choline. Serine is the biochemical precursor of ethanolamine and ethanolamine cephalins can be methylated (with active methionine) to form lecithins (cf. Chapt. VIII-12). The three phosphatides are therefore closely related biogenetically. 

Ethanolamine cephalins are formed in the same way, i.e. ethanolamine is activated with CDP and transferred onto a diglyceride. Cephalins may be methylated to produce lecithins with adenosylmethionine as methyl group donor. This methyla-tion apparently is the main biosynthetic pathway of lecithin and is an important source of choline from ethanolamine (Greenberg and Bremer). 

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