304 LECTURE XIV. 



Let us consider the relations of glycerose to the proteins, or to their 

 building materials. The following formulae will be helpful: 



These formulae show at once what slight differences exist between these 

 apparently entirely distinct groups. It would not be at all difficult to 

 imagine the above three amino acids as being derived from glycerose. 

 Leucine might be produced from one molecule of a hexose or two molecules 

 of glycerose, by the addition of ammonia and partial reduction; 1 and by 

 oxidation, the dibasic glutamic and aspartic acids may be formed from 

 leucine. We meet with certain difficulties when we attempt to account 

 for the formation of these last compounds. Leucine, which is isobutyl- 

 aminoacetic acid, contains a branched chain. The difficulties increase 

 when we come to proteins containing an aromatic ring, such as phenyl- 

 alanine and tyrosine. To produce the benzene nucleus from the carbo- 

 hydrates is a highly complicated process. Such transformations undoubt- 

 edly do occur in the organism of plants, although the formation of these 

 substances is, probably, not a direct one. 



We must also consider the close relation of alanine to lactic acid, which 

 is so easily produced by the action of alkalies or ferments. 



CHOH C 



HNH 2 



COOH COOH 



Lactic acid Alanine 



Plants could also form their albumins or individual amino acids in this 

 manner. Conversely, lactic acid may be easily formed from alanine, 

 serine, and cysteine by disintegration; from alanine, for example, simply 

 by splitting off ammonia. In fact, such processes must take place in the 

 animal organism to a considerable extent. Lactic acid, therefore, may 

 arise from two sources in the animal organism* It may come from carbo- 

 hydrates or from albumin. 



The formation of albumin in the animal organism from the other kinds 



1 Cf. E. Fischer and E. Abderhalden: Z. physiol. Chem. 36, 268 (1902). 



