54 THE PHYSIOLOGY OF PROTEIN METABOLISM 



Evidence from the Fate of Amino Acids. 



Other evidence in support of deaminization being a normal intra- 

 vital change has come from the many experiments which have already 

 been given in detail (p. 44) carried out on the feeding of animals with 

 different amino acids. Thompson (395) found in the case of arginine 

 that the nitrogen was largely excreted as urea ; the amount excreted, 

 however, differed to some extent in the different animals, and apparently 

 with different diets. Part of the urea was excreted at once, part more 

 slowly. He believed the latter the slow excretion came from the 

 deaminization of the ornithine moiety of the arginine molecule. If the 

 arginine were injected subcutaneously there was a much greater pro- 

 portion of its nitrogen excreted as urea. Neuberg and Langstein (304) 

 also showed that after the administration of large doses of alanine to 

 rabbits, lactic acid, the denitrified product, could be found in the urine. 

 The appearance of the oxyacid, lactic acid, is contrary to what one 

 would have expected from the work of Neubauer, who maintains that 

 pyruvic acid, a keto acid, is formed on deaminization of alanine. In 

 experiments which exclude any possible bacterial action, Mayer (281) 

 has shown that after the subcutaneous injection of diamino-propionic 

 acid there was a small output of glyceric acid (a di-oxy acid). The 

 formation of homogentisic acid from tyrosine and phenylalanine in cases 

 of alkaptonuria is direct evidence of deaminization taking place readily. 

 Neubauer and Falta (301) believed that the change consisted in the 

 formation of a keto acid and that the original observation of Blender- 

 mann, that after the administration of tyrosine, p. oxy-phenyl-lactic 

 acid was found in the urine, was wrong. This contention of Neubauer 

 about the keto acid formation, however, is not universally accepted. 

 Kotake (227), for instance, maintained that p. oxy-phenyl-lactic acid 

 could be obtained from the urine only after giving a large amount of 

 tyrosine. Neubauer and Fischer (302) have shown that phenylglyoxylic 

 acid is formed, if the isolated liver be perfused with fluid containing 

 phenylaminoacetic acid. In purine metabolism also deaminization is 

 one of the stages in disintegration as for instance during the conversion 

 of adenine and guanine to hypoxanthine and xanthine. 



