METABOLISM 207 



all food materials are finally converted into this sugar before 

 they are oxidized to yield energy. This has not borne the 

 test of experiment in the case of fats, though we know that in 

 the body fats may be converted into carbohydrates. With 

 the proteins also we are not able to claim that such a trans- 

 formation of the products of protein cleavage into carbohydrates, 

 before oxidation, always takes place, though we can show that 

 such a conversion is possible. 



In the cleavage of proteins alanine or a-amino-propionic acid 

 is one of the normal products, and this by hydrolysis, as already 

 mentioned on page 85, would yield ammonia and lactic acid 

 (a-hydroxy-propionic acid). We know that lactic acid is 

 formed in the body from glucose, such a conversion being simply 

 a spHtting of the molecule without hydrolysis. 



C6Hi206^2 CsHeOs, (CH3-CH(0H)-C00H) 



Glucose Lactic acid 



It would not, therefore, be impossible for the reverse action 

 to occur and glucose to be formed from the lactic acid resulting 

 from the non-nitrogenous portion of protein. That a formation 

 of carbohydrates from protein actually does take place in the 

 animal body has been proved by experiment. It has not been 

 proved, however, that all non-nitrogenous protein cleavage prod- 

 ucts are first converted into carbohydrates before oxidation. 



The actual conversion of proteins into carbohydrates does 

 take place in the body in case there is a lack of carbohydrate 

 and fat food. In such cases the normal supply of glucose in the 

 blood is maintained wholly by protein, and also the glycogen 

 supply in the liver may be similarly kept up. 



Conversion of Proteins into Fats 



That both body fats and milk fats may be formed from pro- 

 teins has been well established by experiment. Whether such 

 a conversion is direct from proteins to fats, or indirect from 

 proteins through carbohydrates to fats, is not so well proved. 



