Constituents of Urine 



These phenolic compounds are not growth-substances. 

 They represent the end-products of normal metabolism of 

 such substances as tyrosine. 



Phenylalanine, a constituent of almost all proteins, is 

 oxidized in the body to phenyl-acetic acid, a growth-substance 

 of considerable potency, and to phenyl-propionic acid. 

 Phenyl-acetic and phenyl-propionic acids can also arise from 

 the metabolism of tyrosine. When fed to animals, phenyl- 

 acetic acid is said to form phenaceturic acid (a bland com- 

 pound of phenyl-acetic acid and glycine) but human beings 

 seem to be peculiar in employing glutamine as the detoxicat- 

 ing agent, forming phenacetoyl-glutamine. 



It is interesting to note that glutamine is used to conjugate 

 phenyl-acetic acid only, and not its derivatives. Some of the 

 urinary phenyl-acetic acid in human urine is combined with 

 glucuronic acid. 



Phenaceturic acid (phenylacetoylglycine), being a com- 

 pound of glycine with phenyl-acetic acid, is analogous to the 

 better-known hippuric acid (benzoyl-glycine) a compound of 

 glycine with benzoic acid. In fact the best natural source for 

 the isolation of phenaceturic acid, as for hippuric acid, is 

 horse urine, and both acids may be isolated from one sample 

 of urine. It appears that the urine of herbivores is richer 

 than that of carnivores in phenaceturic acid. The degraded 

 sweet odour of horse urine is probably referable to its phenyl- 

 acetic acid. 



There seems to be a tendency for aromatic compounds 

 having a fatty acid side-chain to be excreted in urine (in 

 combination with glycine) as either benzoic or phenyl-acetic 

 acid. The substances which, when fed, yielded benzoic acid, 

 were those having an odd number of carbon atoms in the 

 chain (phenyl-propionic, phenyl-valeric acids); while those 

 acids having an even number of carbon atoms (phenyl- 

 butyric, phenyl-caproic) appeared as phenyl-acetic acid. It 

 will be noted that the formation of indole-acetic acid from 

 tryptophan (indole-a-amino-propionic acid) upsets the beauti- 

 ful regularity thus suggested. 



The value of phenaceturic acid as a growth-regulating 



73 



