474 FATE OF BODY-FOREIGN SUBSTANCES 



These findings are the more significant as they suggest the 

 route traversed from the non-nitrogenous products of inter- 

 mediate metabolism to the " building stones " of the protein 

 molecule. For instance, it may easily be imagined that 

 sugar is decomposed into lactic acid in the system, that this 

 is then oxidized to racemic acid and that the latter is changed 

 to alanin by taking up ammonia : 



SUGAR LACTIC ACID RACEMIC ACID ALANIN 



CHj CHj CHj 



CcHuO, * CH.OH * CO > CH.NH t 



COOH COOH COOH. 



It has been actually shown in Embden's laboratory that 

 alanin can be found to appear in a liver rich in glycogen (but 

 not in one which is free of glycogen) in perfusion experi- 

 ments ; if ammonia be added to the perfusing blood in the 

 experiment upon the glycogen-f ree liver, here, too, the recog- 

 nition of alanin-formation is possible. "This is the first 

 time positive proof has been obtained that in intermediate 

 metabolism in the mammal carbohydrate can be transformed 

 into an aminoacid by taking up nitrogen, i.e., can be con- 

 verted into a characteristic component of the protein 

 molecule. " 53 



Acetylizmg Processes m the Animal Body. It has been 

 shown, moreover, that the processes of anabolism and 

 catabolism of the aminoacids in intermediate metabolism 

 are apparently closely connected with acetylization proc- 

 esses. Examples of the attachment of an acetic acid rest to 

 organic substances in metabolism have been known for a 

 long time. Thus furfurol combines in the body with acetic 

 acid to form furfuracrylic acid : 54 



[ J COH + CH 3 .COOH > f | CH = CH COOH. 



""Hanni Fellner (G. Embden'a Lab.), Biochem. Zeitschr., 38, 414, 1912. 

 "According to Jaffe and R. Cohn. 



