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736 URINE.
alanine in the form of polypeptides, from dipeptides as well as tripeptides.
The p-tyrosine and phenylalanine are quantitatively converted into homo-
gentisic acid, in alcaptonuria (Falta). The m- and o-tyrosine, on the
contrary, are not converted, according to Blum,1
into homogentisic acid
in alcaptonurics, and the dibromtyrosine yields just as little homogentisic
acid as the bromine or iodine derivatives of protein bodies (Falta).
According to the investigations of Langstein and Meyer, and especially
of Falta, different proteins yield varying quantities of homogentisic
acid in alcaptonuria, and accordingly larger amounts in proportion as
the protein is rich in tyrosine and phenylalanine.
On this account the quotient H ( = homogentisic acid):N (nitrogen)
is variable on the introduction of different proteins. For example, with
casein H : N is on an average much higher than with white of egg. In
most of the cases of alcaptonuria examined the H : N was equal to
40-50: 100, and with the same alcaptonuric, when no essential change
in the diet occurs, the quotient is relatively constant.
Wolkow and Baumann explain the formation of homogentisic acid
from tyrosine by an abnormal fermentation in the upper parts of the
intestine, but this view has now been generally rejected. The observa-
tions of Aberhalden, Bloch and Rona 2
that glycyl-Z-tyrosine on
subcutaneous injection causes an increased formation of homogentisic
acid, disproves this theory, and indicates a formation of homogentisic
acid in the tissues. This acid is also burnt in the healthy organism if
not too large quantities of the acid are introduced at one time, and it is
the general view that alcaptonuria is an anomaly in the protein metabolism.
In order to understand this anomaly and the origin of the homogentisic
acid we must call attention to the fact that the investigations of O.
Neubauer and Falta, Langstein and others 3
show that only such
aromatic acids are converted, in the body, into homogentisic acid, which
have a three-membered side-chain which is substituted by NH2 ,
OH
or in the a-position to the carboxyl group and not in the ^-position,
p-tyrosine, phenylalanine, phenyl-a-lactic acid and phenyl-pyroracemic
acid are such acids. It can be admitted with Falta that the phenyl-
alanine in the body by deamidation is converted into phenyl-a-lactic
acid, CeH5.CH2.CHOH.COOH, from which by taking up two hydroxyl
groups, dioxyphenyl-a-lactic acid (uroleucic acid), (OH)2CeH3.CH2.
CHOH.COOH, is formed, and then from this by oxidation dioxyphenyl-
acetic acid (homogentisic acid), (OH) 2 C6 H3.CH2 .COOH, is produced.
Tyrosine is also supposed to undergo an analogous transformation
x
Arch. f. exp. Path. u. Pharm., 59.
2
Zeitschr. f. physiol. Chem., 52.
* Ibid., 42; Frornherz, 1. c.
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