FATS AND OILS, WAXES, AND LIPOIDS 143 



Again, the choline may be attached to the phosphoric acid either 

 through its alcoholic (OH) group or through its basic (OH) group, 

 thus 



OH /OH 



P^O 



\0-N=(CH 3 ) 3 

 or, 



The facts that in the arrangement (B) the central carbon atom of 

 the glycerol would be asymmetric, and that both lecithin and the 

 glycero-phosphoric acid derived from it by hydrolysis are optically 

 active, prove that formula (B) correctly represents the arrange- 

 ment of that part of the lecithin molecule; and there is ample 

 theoretical and experimental evidence to prove that the choline 

 linkage is through the alcoholic (OH) group. Hence the formula 

 for lecithin indicating the linkage as shown above is the correct one. 

 The fatty acids in the lecithin molecule may be different in 

 lecithins from different sources, just as they are different hi fats 

 from different sources. Both oleic acid and a solid fatty acid have 

 been found in the hydrolysis products of lecithin from leguminous 

 seeds. In certain lupine seed, the fatty acids present in the lec- 

 ithin appear to be palmitic and stearic. 



OTHER PLANT PHOSPHATIDES 



Phosphatides other than lecithin are common in plants. In 

 these, various sugars replace part or all of the glycerol as the alco- 

 holic part of the ester. Percentages of sugar varying from mere 

 traces up to 17 per cent of the weight of material taken, have been 

 found in the products of hydrolysis of phosphatides prepared 

 from vetch seeds, potato tubers, plant pollens, and whole wheat 

 meal. 



Furthermore, betaine 



(tri-methyl glycocoU, OC/ N >N=(CH 3 ) 3 ) 



^ O / 



and perhaps other vegetable amines (see Chapter XII) sometimes 

 replace choline as the basic group in the phosphatides. 



