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COMPOUND PROTEINS. 167
titatively into carbaminoacids. With the diamino-acid arginine, which
contains 4 nitrogen atoms, it is on the contrary only one-fourth because
this acid reacts with only one amino group, that of the a-amino valeric
acid chain.
The reaction which has been developed and extensively used by
Siegfried 1
and his pupils is of great value in the characterization of pep-
tones, kyrines, and proteoses, for the separation and fractional pre-
cipitation and for the determination of their constitution. The binding
of the carbon dioxide as carbamino-salts seems also in many ways
to be of physiological importance, as for example, the solubility of cal-
cium carbonate in alkaline fluids and for the carbon dioxide binding in
blood, etc.
The amino-acids can by methylation form betaines, for example,
trimethyl glycocoll or betaine CH2—N(CH3)3. Betaine occurs abundantly
CO
in the plant kingdom. In the animal kingdom such bodies have been
found under physiological conditions in cold blooded animals and they
belong to those groups of bodies which have been called " aporrhegmas"
by Ackermann and Kutscher.2
As " aporrhegmas " they designate
all those fractions of amino-acids from the protein, which can be pro-
duced from the proteins in a physiological manner and indeed in the life
of animals as well as the plants. These bodies are essentially the same
as have been observed in the putrefaction of the amino-acids and which
have been specially mentioned with every amino-acid described.
The behavior of the amino-acids in yeast fermentation will be dis-
cussed in Chapter III.
In regard to the methods for separating and preparing, in a pure form,
the various amino-acids and other products of protein hydrolysis which
have not been given in the preceding pages, we must refer to Abderhal-
den’s Handbuch der biochemischen Arbeitsmethoden, 1909-1910 Bd. 2.
II. Compound Proteins.3
We designate as compound proteins those bodies which yield, on
cleavage, proteins (with their decomposition products) and other bodies
such as carbohydrates, nucleic acids, or pigments.
The compound proteins known at present can be divided into three
groups: glycoproteins, nucleoproleins and chromoproteins. Of these the
1
In regard to the literature see Siegfried in Ergebnisse d. Physiol. Bd. 9.
2
Zeitschr. f. physiol. Chem., 69. See also Engeland, ibid., 69.
3
Hoppe-Seyler has given the name proteide to these compound proteids, but as
this term is misleading in English we do not use it in English classifications in this
sense.
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