METABOLISM 167 



235. Formation of carbohydrates from proteins. It has 



already been stated (216) that carbohydrates may be manu- 

 factured, in the bodies of carnivorous animals at least and 

 probably in those of other species, but the question whether 

 the proteins or the fats or both serve as the source was left 

 open. 



Without entering into experimental details, it may be stated, 

 as the general result of many trials in which the possibility 

 of a production from fats was excluded as completely as pos- 

 sible, that carbohydrates have been produced in such large 

 amounts, and in quantities so closely paralleling the quantities 

 of protein katabolized, as to amount to a proof of their formation 

 from the latter. The acceptance, however, of the view that 

 carbohydrates may be a product of protein katabolism by no 

 means excludes the possibility of their formation also from fats. 

 Indeed, in view of the importance of carbohydrates in metab- 

 olism it seems altogether likely that the body has the power 

 to manufacture them from both fats and proteins, while, as 

 already stated (217), the reverse process of the formation of 

 fats from carbohydrates has been demonstrated. 



With the increasing knowledge of the details of protein 

 katabolism afforded by recent investigations, the question 

 under consideration has assumed a somewhat different aspect, 

 the discussion shifting from the fate of the proteins as a whole 

 to that of the single amino acids and of the non-nitrogenous 

 products of their katabolism. It has been shown, especially 

 by the work of Lusk and his associates, that some at least of the 

 amino acids (glycin, alanin, aspartic acid, glutamic acid, histi- 

 din), after deaminization may yield dextrose. In the case of 

 glycin and alanin all the carbon of the amino acid could be re- 

 covered in the form of dextrose. In the case of aspartic and 

 glutamic acids, on the other hand, only three out of the four or 

 five carbon atoms respectively were found in the dextrose pro- 

 duced. Still other amino acids, notably leucin and tyrosin, 

 apparently do not yield dextrose, but instead compounds like 

 /3 hydroxybutyric acid and aceto-acetic acid which are the 

 distinctive products of the katabolism of the higher fatty acids 

 (252). 



In the case of some, then, but apparently not all, of the prod- 

 ucts of protein katabolism, the relations between protein and 



