Constituents of Urine 



Chemists may wonder how tyrosine (p-/>-hydroxy-phenyl-a- 

 amino-propionic acid) and phenyl-alanine (^-phenyl-a- 

 amino-propionic acid) acquire the 2:5 hydroxy groups. 

 It may be stated that proof of the physiological origin of 

 2 : 5-dihydroxy-phenyl-acetic acid from both tyrosine and 

 phenyl-alanine rests upon the increased excretion of homo- 

 gentisic acid after ingestion of either of the amino-compounds 

 by an alcaptonuric. 



Alcaptonuria is too rare a condition to have an agricultural 

 importance, but consideration of it suggests that the black 

 matter of manure- and compost-heaps may be in part a 

 complex of oxidation products of dihydroxyphenols. For 

 further information about the acid, see the section "Nachweis 

 and Bestimmung der Homogentisinsaure im Harn", by W. 

 Weise, in Abderhalden's Handbuch (193 1), Abt. 4, Teil 



5 (i). 551-560. 



Coupling of a ring-acid with an ahphatic amino-acid 

 (conjugation) seems to be of a fairly general occurrence. The 

 methyl-pyridine compounds in 2-methylpyridine and pico- 

 linic acid, after administration by mouth, appears in the urine 

 of dogs, rabbits, and frogs, as pyridinuric acid, a compound of 

 picolinic acid and glycine, analogous to phenaceturic and 

 hippuric acids. 



Picolinic acid administered to birds becomes combined with 

 the peculiar avian detoxicating amino-acid, ornithine, and is 

 excreted as pyridinornithuric acid. Ornithine is normally 

 found in combination with benzoic acid as ornithuric acid, 

 but acetyl-ornithine has been reported as a plant constituent 

 by Manske. 



Indoxyl (hydroxy-indole) and skatoxyl are other phenols 

 found in urine, of carnivora particularly. They are usually 

 conjugated in the form of potassium sulphates; the indoxyl 

 potassium salt is known as urine-indican. Their effect on 

 plants is not known. Indole-propionic acid is stated to undergo 

 hydroxylation before excretion. 



3-indole-acetic acid is the substance revealed by the old 

 "urorosein" test (see Chapter XIV). Its properties and a brief 

 account of its isolation from urine are given elsewhere. 



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