FURTHER FATE OF AMINO ACIDS 115 



pathological nature, but should be looked upon rather 

 as an anomaly of metabolism and is generally con- 

 sidered as being hereditary in origin. It occurs oftener 

 in man than in woman and blood relationship, as first 

 cousins, predisposes to the condition. 



Whenever homogentisic acid is present in the urine, 

 it is there in relatively large amounts for the anomaly 

 is an absolute one, that is, apparently homogentisic 

 acid formed is destroyed by the normal organism. 

 The relationship of tyrosine phenylalanine and homo- 

 gentisic acid are shown below : 



OH 



CH, 

 CH.NH, 



COOH 

 Tyrosine Homogentisic acid 



Phenylalanine 



The significance of alkaptonuria in connection with 

 the metabolism of the amino acids is that the appear- 

 ance of homogentisic in the urine of alkaptonurics 

 gave the first hint as to the probable transformations 

 occurring in the demolition of the benzene radical 

 found in tyrosine and phenylalanine. That homogen- 



