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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 amino-acids, is first transformed into the corresponding keto-
acid, p-oxyphenyl pyroracemic acid, OH.CeH4.CH2.CO.COOH, which
is then oxidized into the corresponding chinol and transformed into
hydroquinone pyroracemic acid, (OHjoCeHs.Cr^.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 hydroxy! groups in
the side chain of the two bodies, as shown by the formulae HO<f yOH (homo-
CH-COOH
OH
gentisic acid) and ( y (tyrosine) do not exist now, since we have
CH,CHNH,COOH
learnt of other analogous processes. For example, the oxidation, by Kumagai and
"Wolffensteix, 2
of paracresol H3C\ /OH with potassium persulphate in
OH
acid solution. In this manner the expected 3.4 dioxytoluene H3C<
was not obtained, but instead homohydroquinone HO<f /OH, and hence a
CH,
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 /-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. (1. d. Chem. Gesellsch., 41.
’ Zeitschr. f. physiol. Chem., 77.
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