504 V. CHEMISTRY OF PHOSPHATIDES AND CEREBROSIDES 



and are apparently monobasic acids. They do not reduce Fehling solution, 

 and no free amino nitrogen is present. They are levo-rotatory ([aji, 

 (pyridine) = -2.79°). 



On hydrolysis, the ganglioside from brain yields the following products; 

 fatty acids, 20%; sphingosine or sphingosine-like base, 13%; neuraminic 

 acid, 21%; and sugar, which is galactose, 40-43%. Klenk^^^ suggests the 

 following eciuation for the hydrolysis : 



C64H„sN20,6 + 5 H.O > CisHseOo + CH^NOo + C.oH.gNOs + 3 CeHi.Oe 



Ganglioside Stearic Sphingosine Neuraminic Galactose 



acid acid 



Apparently more than one ganglioside exists, since differences in fatty 

 acid composition are noted. While human brain ganglioside contains 

 exclusively stearic acid, only neuraminic acid is found in that isolated from 

 the spleen^''" The hydrolysis of beef spleen ganglioside differs somewhat 

 from the reactions observed with brain cerebroside: 



C7oH,3oN20,6 + 5 H.O > C.4H48O2 + C18H37NO2 + C10H.0NO9 + 3 CeH.oOe 



Ganglioside Lignoceric Sphingosine Neuraminic Galactose 



acid acid 



a. Neuraminic Acid. Neuraminic acid was first obtained in crystalline 

 form by Klenk'*'-'- in 1941 . This acid is presumably the group in the ganglio- 

 side molecule responsible for the characteristic color reactions of the 

 gangliosides, as well as for their property of charring when heated with di- 

 lute mineral acid. It is a monobasic acid with an empirical formula of Cio- 

 HigNOg or C10H19NO9. It possesses a strong levo-rotation ([a]o = 

 — 54.91°). It is easily soluble in water but only slightly soluble in metha- 

 nol and completely insoluble in ethanol and diethyl ether. 



Neuraminic acid has a primary amino group, and it gives a positive nin- 

 hydrin reaction. Although it decomposes on heating with acids, under 

 which condition it yields a bromi-colored solution, it is stable when heated 

 in neutral or alkaline solution. It develops an intense red color with Bial 

 reagent. When heated with Ehrlich reagent at 140°C., it displays a strong 

 red color which is positive in amounts as small as 60 Mg-^" This acid does 

 not reduce an alkaline copper solution. Whether neuraminic acid occurs in 

 brain lipids other than in the gangliosides is not known. However, its pres- 

 ence in these latter compounds seems to be well substantiated. 



(^) Cerebrosides Containing Two Sugar Molecules 



In addition to the regular cerebrosides, which contain only one carbohy- 

 drate group, and the gangliosides, which have three carbohydrate molecules, 

 Klenk and Rennkamp''^- have isolated an intermediate compound from 



«i E. Klenk, Z. physiol. Chem., 273, 76-86 (1942). 

 «2 E. Klenk, Z. physiol. Chem., 268, 50-58 (1941). 



