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738 URINE.
acid or any other intermediary product of the cleavage of tyrosine in
the urine after taking 150 grams /-tyrosine (of which 141 grams were
absorbed)
.
Dakin l
has recently opposed the above-mentioned view that in the
cleavage of tyrosine and phenylalanine, homogentisic acid is always
produced, and that the condition of alcaptonuria consists in an inability
of the body to burn this intermediary product of metabolism. He has
found that tyrosin-methyl ether, which cannot form any quinone-like
intermediary product, can in cats be just as completely burnt as tyrosine,
and the same is true for p-methylphenylalanine and for p-methoxy-
phenylalanine, which cannot form any quinone derivatives. Still
these substances can be completely burnt by alcaptonurics and accord-
ing to Dakin the body in alcaptonuria has still the ability to completely
burn the aromatic nucleus of tyrosine and phenylalanine when the
transformation into homogentisic acid is prevented by a proper sub-
stitution in the para-groups. Dakin therefore considers alcaptonuria
as a condition in which partly the formation of an abnormal metabolic
product—the homogentisic acid—takes place and where partly the ability
of the body to burn this product is diminished.
Garrod,2
who has observed several cases of alcaptonuria, has also
tabulated a large number of cases of alcaptonuria which he finds in the
literature, and he shows that the anomaly of the protein metabolism
occurs oftener in males than in females, and also that blood relationship
of the parents (first cousins) predisposes to alcaptonuria.
On fusing homogentisic acid with alkali it yields gentisic acid (hydro-
quinone-carboxylic acid) and hydroquinone. When introduced into the
intestine of the dog a part is converted into toluhydroquinone, which
is eliminated in the form of an ethereal sulphuric acid. Homogentisic
acid has also been prepared synthetically by Baumann and Frankel,
starting with gentisic aldehyde, and by Neubauer and Flatow 3
from
o-oxyphenylglyoxylic acid with hydroquinone glyoxylic acid and hydro-
quinone glycollic acid as intermediary bodies.
Homogentisic acid crystallizes with 1 mol. of water in large, trans-
parent prismatic crystals, which become non-transparent at the tem-
perature of the room with the loss of water of crystallization. They
melt at 146.5-147° C, and are soluble in water, alcohol, and ether, but
nearly insoluble in chloroform and benzene. Homogentisic acid is
1
Journ. of Biol. Ohem., 8 and 9, with Wakeman, ibid., 9.
2
Med. chirurti. Transact., 1899 (where all cases up to that time are tabulated);
also The Lancet, 1901 and 1902; Garrod and Hele, Journ. of Physiol., 33.
3
Baumann and Friinkel, Zeitsohr. f. physiol. Chem., 20; Neubauer and Flatow.,
ibid., 52.
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