HOMOGENTISIC ACID. 737 



whereby a removal of the OH group in the para position must be 

 admitted. 



According to NEUBAUER, 1 on the contrary, the tyrosine, as well as 

 the other ammo-acids, is first transformed into the corresponding keto- 

 acid, p-oxyphenyl pyroracemic acid, OH.C6H 4 .CH 2 .CO.COOH, which 

 is then oxidized into the corresponding chinol and transformed into 

 hydroquinone pyroracemic acid, (OH^CeHs.CH^.CO.COOH. The homo- 

 gentisic acid is derived from this latter by the splitting off of carbon 

 dioxide by oxidative means. Phenylalanine is either changed into 

 phenyl pyroracemic acid or into p-oxyphenyl pyroracemic acid with 

 tyrosine as intermediary body and then changed as above stated. 



According to the accepted hypothesis the demolition of tyrosine 

 and phenylalanine takes place into homogentisic acid, and the anomaly 

 in the metabolism of alcaptonurics consists in that in these the demoli- 

 tion stops at this point and that the ability to rupture the benzene ring 

 is absent, in the organism, in alcaptonuria. 



,The difficulties in accepting the assumption of a transformation of tyrosine 

 into homogentisic acid due to the different positions of the hydroxyl groups in 



the side chain of the two bodies, as shown by the formulae HO^ yOH (homo- 



\ / 



CH,COOH 

 OH 



gentisic acid) and \^ "/ (tyrosine) do not exist now, since we have 



CH 2 CHNH 2 COOH 

 learnt of other analogous processes. For example, the oxidation, by KUMAGAI and 



WoLFFENSTEiN, 2 of paracresol H 3 C<f /OH with potassium persulphate in 



OH 

 acid solution. In this manner the expected 3.4 dioxytoluene H 3 C<f y>OH 



was not obtained, but instead homohydroquinone HO<T /OH, and hence a 



CH 3 



transference of the alkyl group must have occurred. 



ABDERHALDEN 3 has also shown in healthy human beings that tyrosine 

 may cause an elimination of homogentisic acid, as he positively detected 

 a small quantity of homogentisic acid in the urine of a man who had 

 taken 50 grams Z-tyrosine per os (of which 44 grams were absorbed). 

 In the urine of another man he could not detect either homogentisic 



1 Cited from Centralbl. f . Physiol, 23, 76. 



2 Ber. d. d. Chem. Gesellsch., 41. 

 8 Zeitschr. f. physiol. Chem., 77. 



