318 LECTURE XIV. 



tionably does not synthesize albumin from carbohydrates. It does not 

 follow that the reverse process may not take place. We must also remem- 

 ber that the proteins contain large complexes, the nature of which we know 

 but little. It is possible that more complicated hydroxy-acids, such as di- 

 amino-tri-hydroxy-dodecoic acid, 1 are present, the conversion of which 

 into carbohydrates would be easy to understand. At all events, we must 

 admit that the conversion of amino acids into sugars is no more difficult to 

 understand than is the transformation of fatty acids into carbohydrates, 

 and conversely. The formation of sugar from amino acids is connected 

 with the question as to what becomes of the carbon of the amino acids 

 which does not leave the organism in the form of urea. When the func- 

 tion of these nitrogen-free carbon chains is explained, the problem of the 

 sugar formation of sugar from albumin will be less difficult to solve. This 

 is the vital point of the whole question, and from this standpoint the whole 

 subject must be considered. 



We might think that feeding amino acids alone would show, in the first 

 place, whether they have any effect upon the formation of glycogen; and 

 secondly, whether they effect the elimination of sugar. Such experiments 

 have, in fact, been made. Alanine and leucine, on account of their having 

 respectively three and six carbon atoms in the molecule, seemed especially 

 suited for the experiment, although the latter has a methyl side chain. 

 It is well known that normal carbon chains of the carbohydrates can easily 

 go over into branching chains, for example, in the formation of saccharine; 

 and so, on the other hand, we can imagine the possibility of the reverse 

 process taking place in the transformation of leucine into a sugar. The 

 experiments which have been performed in this direction are very con- 

 tradictory, and have led to no positive conclusions, 2 although apparently 

 the feeding of individual amino acids, in particular leucine and alanine, 

 does not cause any accumulation of glycogen. 



This does not by any means preclude the possibility of sugars being 

 produced from amino acids. We can easily imagine that the disintegration 

 of the amino acids from a protein proceeds in its intermediate stages in a 

 different manner from that which takes place when we feed large amounts 

 of the individual amino acids, as such, to the organism. We know very 

 little as yet about the intermediate disintegration of albumin, and are 

 unable to state whether the amino acids, as such, are set free, or whether 

 the disintegration of the proteins does not take place after the removal 



1 E. Fischer and E. Abderhalden: Z. physiol. Chem. 42, 540 (1904). 



2 Cf. E. Pfluger's criticism (Glycogen, loc. cit.}. R. Cohn, Z. physiol. Chem. 28, 211 

 (1899), found that feeding rabbits with leucine caused an increase of over 400 per cent of 

 glycogen, whereas O. Simon, ibid. 35, 315 (1902), found no glycogen formation to take 

 place. Grube (Pfluger's Arch. 118, 1 (1907) ) also came to the conclusion, from experi- 

 ments with the livers of turtles, that leucine and alanine did not increase the glycogen 

 content. 



