2o6 ORGANIC AGRICULTURAL CHEMISTRY 



By the further oxidation of these products we would obtain 

 carbon dioxide and water from the carbon-hydrogen-oxygen 

 portion, the ammonia remaining as ammonia. From our study 

 of the chemistry of urea in Section I (p. 97) we know that urea 

 may be synthesized from ammonia and carbon dioxide. Thus 

 part of the carbon dioxide of the complete oxidation would 

 remain combined with the ammonia as urea. This explains what 

 we shall later consider again, that the theoretical calorific value 

 or energy value of protein is not obtained in the animal body, 

 because a part of this energy is lost in urea and the other nitro- 

 gen compounds of urine. In practice, therefore, we subtract 

 from the theoretical calorific value of protein the calorific value 

 of the urine to obtain the physiological or body calorific value 

 of protein. 



This would seem to indicate that in the katabolism of protein 

 a hydrolytic cleavage of the molecule into a nitrogenous un- 

 oxidizable portion and a non-nitrogenous oxidizable portion 

 must precede the oxidation, for if the oxidation occurred with 

 the protein molecule before splitting, we should expect all of 

 the carbon and hydrogen to be oxidized, and the body calorific 

 value of proteins would be more nearly equal to the value ob- 

 tained in a combustion calorimeter. 



Conversion of Proteins into Carbohydrates 



What now happens to this non-nitrogenous portion of the 

 protein molecule? We know that such a portion would be 

 capable of immediate oxidation and we know also that even- 

 tually it is completely oxidized, though not all of its energy of 

 oxidation is liberated, some of the carbon dioxide combining 

 with the ammonia, the other hydrolytic product of the protein, 

 yielding urea. Whether the oxidation of the non-nitrogenous 

 portion takes place immediately or whether other metabolic 

 changes occur before oxidation is not clear. 



It has been claimed that all of the oxidation in the body by 

 which energy is liberated is the oxidation of glucose and that 



