THE LECITHINS 417 



found that the lecithin-ghicose compounds, which are loosely l)Ound 

 products, have a quite variable composition. This fact raises the question 

 as to whether or not they should be considered as true compounds. '^^ 



The combination of lecithin with protein has been widely accepted, since 

 such lecithoproteins were first obtained from egg-yolk by Hoppe-Seyler,''^ 

 as well as by WeyV^ and more recently by Osborne and Campbell.*" 

 Lecithoproteins are soluble in salt solution, and they precipitate on dialysis 

 or on dilution with water. The lecithin cannot be extracted with water, 

 but it can be removed with alcohol. Synthetic lecithoproteins, soluble 

 in chloroform, have been prepared with ovalbumin*^ and casein.*^ De 

 Jong and Westerkamp*^ questioned the chemical nature of such conjugate 

 proteins, since combination occurred only within the range of their iso- 

 electric points when they had opposite electrical charges. Such a com- 

 bination would thus appear in all probability to be an adsorption complex 

 rather than a chemical compound. 



Since lecithins almost invariably contain unsaturated fatty acids, they 

 are capable of adding the halogens. Thus, on treatment with bromine, 

 octobromo- and hexabromolecithins have been prepared from liver, and a 

 tetra- and dibromide from egg lecithin.** On hydrolysis, octabromara- 

 chidic, hexabromostearic, and tetrabromostearic acids were prepared, 

 indicatmg that the unsaturated double bonds were present in the con- 

 stituent fatty acids. The iodine numbers obtained wiih various lecithin 

 preparations obviously depend upon the unsaturated acids represented, 

 and will vary from 33 to 127 for the common lecithins. However, since 

 oxidation results so readily when lecithin is exposed to air, with the con- 

 sequent obliteration of the unsaturated linkages, the iodine number is of 

 value only when the lecithin is so prepared that oxidatioir is scrupulously 

 avoided. The theoretical values for the iodine numbers of some lecithins 

 are given in Table 3, together with results obtamed by Levene and co- 

 workers with some of their pure preparations. 



Because of the unsaturated bonds, lecithin will also adfl hydrogen to 

 form hydrolecithin. Hydrogenation is brought about by treating an al- 

 coholic solution of lecithin with hydrogen in the presence of a colloidal 

 palladium catalyst. Pure hydrolecithin was first prepared by Ritter*'; 

 the only fatty acid obtained from it on hydrolysis was stearic acid. Ceph- 

 alin-free hydrolecithin was also prepared from egg-yolk*^ and brain, ^^ 



^8 F. Iloppe-Seyler, Med.-Chem. Unlersuch., 2, 215-220 (1867). 



"« T. Weyl, Z. physiol. Chem., 1, 72-100 (1877-1878). 



*' T. B. Osborne and G. F. Campbell, J. Am. Chem. Soc, 22, 413-422 (1900). 



»i G. Galeotti and G. Giampalmo, Arch.fisiol., 5, 503-519 (1908). 



82 T. R. Parsons, Biochem. J., 22, 800-810 (1928). 



83 H. G. B. De Jong and R. F. Westerkanip, Biochem. Z., 234, 367-400 (1931). 

 8^ P. A. Levene and I. P. Rolf, /. Biol. Chem., 67, 659-666 (1926). 



85 F. Ritter, Ber., 47, 530-532 (1914). 



86 P. A. Levene and C. J. West, /. Biol Chem., 33, 111-117 (1918); 34, 175-186 

 (1918). 



