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OXYPROTEIC ACIDS. 755
Liebermann x
this acid is not a unit substance, and contains a part of
its sulphur as ethereal sulphuric acid, and it also contains uroferric acid.
Tho urochrome, which has been specially studied by Dombrowski, 2
is con-
eidered by him and Bondzynski us belonging to the oxyproteic acid group. I
contains about 5 per cent sulphur, is precipitated by copper acetate and yields
melanin-like substances on its decomposition. No positive proofs arc at hand in
regard to the purity of this urochrome and the reports as to its composition,
which are very contradictory, do not exclude the possibility that this is a mixture
of a yellow pigment with another substance (see page 741).
Browinski and Dombrowski 3
have carried out investigations on the nitrogen
tit ratable with forniol on the oxyproteic acids before and after acid hydrolysis.
They found that the antoxyproteic acid and the oxyproteic acid did not contain
any nitrogen split off as NH3 by MgO before hydrolysis, while the alloxyproteic
acid as well as the urochrome yielded about 3 per cent of the total nitrogen in this
form. After acid hydrolysis all gave about the same quantity of ammonia. The
two first-mentioned acids, especially oxyproteic acid, were before hydrolysis
considerably richer in amino groups, tit ratable with formol, than the others.
This indicates that these two acids are produced from the proteins by a deeper
cleavage than is the alloxyproteic acid. The large amount of free amino groups,
which occur especially in the oxyproteic acid and which amount to 38.8 per cent
of the total nitrogen, is nevertheless remarkable.
The preparation of the three above-mentioned acids is based in part
upon the fact that alloxyproteic acid alone is precipitated by basic lead
acetate and that the two other acids can be precipitated from the fil-
trate by mercuric acetate, the antoxyproteic acid in acetic acid solution
and the oxyproteic acid in neutral solution. The preparation is never-
theless very tedious and complicated and therefore we must refer to the
original works for details.
Uroferric acid is an acid isolated by Thiele 4
from the urine, according to
Siegfried’s method for preparing pure peptone. It also contains sulphur, 3.46
per cent, and has the formula CssHseXsSOig. The acid forms a white powder
which is readily soluble in water, saturated ammonium-sulphate solution, and
methyl alcohol. It is soluble with difficulty in absolute alcohol, insoluble in benzene,
chloroform, ether, and acetic ether. About one-half of the sulphur can be split
off as sulphuric acid on boiling with hydrochloric acid. The acid gives neither
the biuret test nor Millon’s or Adamkiewicz’s reactions. It is precipitated by
mercuric nitrate and sulphate, and also by phosphotungstic acid. This acid is
hexabasic, and its specific rotation at 18° C. (a)o = —32.5°. On cleavage it
yields melanine substances, sulphuric acid, aspartic acid, but no hexone bases.
The existence of this acid is disputed by Bondzynski, Dombrowski and Panek.
The investigations of Ginsberg also contradict the occurrence of such an acid,
because no sulphuric acid could be split off from the mixture of the oxyproteic
acids by hydrolysis.
Methods for the quantitative estimation of the total oxyproteic
acids have been suggested by Ginsberg and by Gawinski.5
Accord-
1
Zeitschr. f. physiol. Chem., 52.
2
Ibid., 46 and 62.
3
Ibid., 77.
4
Zeitschr. f. physiol. Chem., 37.
5
Ginsberg, Hofmeister’s Beitrage, 10; Gawinski, Zeitschr. f. physiol. Chem., 58.
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