Serine cephalins

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. 

Phosphatidylethanolamine (cephalin) and ph os-phatidylserine (found in most tissues) differ from phosphatidylcholine only in that ethanolamine or serine, respectively, replaces choline (Figure 14-8). 

Phosphatidylcholine (lecithin) is the most abundant phospholipid in membranes. Phosphatidylethanolamine (cephalin) has an ethanolamine residue instead of choline, and phosphatidylserine has a serine residue. In phosphatidylinositol, phosphatidate is esterified with the sugarlike cyclic polyalcohol myo-inositol. A doubly phosphorylated derivative of this phospholipid, phosphatidylinositol 4,5-bisphosphate, is a special component of membranes, which, by enzymatic cleavage, can give rise to two second messengers, diacylglycerol (DAG) and inositol l,4,5trisphosphate (InsPsi see p.386). 

Serine Phosphatidyl serine Ethanolamine Phosphatidyl ethanolamine (a-cephalins)... 

Cephalins are glycerophospholipids present in foods. They differ from lecithins by having ethanolamine or serine instead of choline in their structure. Could you differentiate between lecithins and cephalins on the basis of the three tests to be performed in this experiment ... 

Folch, J. (1942) Brain cephalin, a mixture of phosphatides. Separation from it of phosphatidyl serine, phosphatidyl ethanolamine and a fraction containing an inositol phosphatide, J. Biol. Chem. 146, 35-44. 

Properties Yellowish, amorphous substance characteristic odor and taste. Insoluble in water and acetone soluble in chloroform and ether slightly soluble in alcohol. A group of phospholipids in which two fatty acids (Rt and R2) form ester linkages with the two hydroxyl groups of glycerophosphoric acid, and either ethanolamine or serine (Rj) forms an ester linkage with the phosphate group. Cephalins are therefore either phosphatidylethanolamine or phosphatidylserine. They are associated with lecithins found in brain tissue, nerve tissue, and egg yolk. 

Phosphatidic acids are the simplest phosphoacylglycerols and are present only in small amounts in membranes. The most common phosphoacylglycerols in membranes have a second phosphate ester linkage. The alcohols most commonly used to form this second ester group are ethanolamine, choline, and serine. Phosphatidylethanolamines are also called cephalins, and phosphatidylcholines are called lecithins. Used as emulsifying agents, lecithins are added to foods such as mayonnaise to prevent the aqueous and fat components from separating. 

The classification of a phosphatidyl ester depends on the nature of the second alcohol esterified to the phosphoric acid. Some of the most important lipids in this class are phosphatidyl ethanolamine (cephalin), phosphatidyl serine, phosphatidyl choline (lecithin), phosphatidyl inositol, phosphatidyl glycerol, and diphosphatidyl glycerol (cardiolipin) (Figure 8.5). In each of these types of compounds, the nature of the fatty acids in the molecule can vary widely. All... 

Phosphoglycerides in which the alcohol is ethanolamine or serine, rather than choline, are called cephalins. They are found in most cell membranes and are particularly abundant... 

They differ in the identity of the amino alcohol portion. Lecithins contain choline, and cephalins contain ethanolamine or serine. 

Lecithin, (10.47a), is fonnd in egg yolk, brain tissue and skin. The ethanolamine (10.47b) and serine (10.47c) derivatives, known as cephalins, exist as zwitterions in their physiological environment of pH 7. 

Phosphoglycerides consist of glycerol esterified to two fatty acids and phosphoric acid. The phosphoric acid is further esterified to choline (in the lecithins) and to etha-nolamine or serine (in the cephalins). The phosphoglycerides are particularly important in membrane formation. 

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. These three compounds are closely interrelated in the body and, in fact, appear to form part of a metabolic cycle which may be represented as shown in Fig. 1. 

Phosphatidyl Ethanolamines (Cephalins) These glycerophospholipids have previously been named cephalins. However, it is now known that, in addition to phosphatidyl ethanolamine, phosphatidyl serine and phosphatidyl inositol also... 

Complete fractionation of brain cephalin Isolation from it of phosphatidyl serine, phosphatidyl ethanolamine, and diphosphoinositide. J. biol. Chem. 177, 497 (1949). 

Subjects i 1 Lipid- phosphorus 1 Le-1 cithin 1 Sphin-1 go-myelin Ethanol- amine- cephalin Serin- cepha- lin Lyso- lecithin Total recov- ery... 

A mixture of phosphatidyl serine and phosphatidyl ethanolamine was once referred to as cephalin. 

The common nitrogenous components associated with the phospholipides in animal tissues are choline (in lecithin), j3-aminoethyl alcohol (in cephalin), serine (also in cephalin), and spbingosine (in sphingomyelin). Lecithin and sphingomyelin are apparently the principal phospholipides of the plasma of man and dog. " Cephalins are practically absent from the plasma of man, dog, and beef, but considerable amounts are found in... 

Cohtmine is of interest as being a constituent of the cephalins (p. 167), and a possible precursor of the cholines. Its natural origin is unknown, the simplest source being decarboxylation of the hydroxy-amino acid, serine. 

---