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CHAPTER II.
THE PROTEIN SUBSTANCES.
The chief mass of the organic constituents of animal tissues consists
of amorphous nitrogenized, very complex bodies of high molecular weight.
These bodies, which are either proteins in a special sense or bodies nearly
related thereto, take first rank among the organic constituents of the
animal body on account of their great abundance. For this reason they
are classed together in a special group which has received the name
protein group (from irpayrtvw, I am the first, or take the first place).
The bodies belonging to these several groups are called protein sub-
stances, although in a few cases the protein bodies in a special sense are
designated by the same name.
The several protein substa?ices x
contain carbon, hydrogen, nitrogen, and
oxygen. The majority contain also sulphur, a few phosphorus, and a
few also iron. Copper, chlorine, iodine, and bromine have been found
in some few cases. On heating the protein substances they gradually
decompose, producing a strong odor of burned horn or wool. At the same
time they produce inflammable gases, water, carbon dioxide, ammonia,
and nitrogenized bases, besides many other substances, and leave a large
quantity of carbon. On deep hydrolytic cleavage they yield abundance
of a-monamino-acids of various kinds as decomposition products.
The nitrogen occurs in the protein bodies in various forms, and this
is also revealed in the division of the nitrogen among the cleavage prod-
ucts. On boiling with dilute mineral acids we obtain (1) so-called amide
nitrogen, which is readily split off as ammonia; (2) a guanidine residue
which is combined with diaminovaleric acid as arginine, and which
has also been called the urea-forming group; (3) basic nitrogen or diamino-
acid nitrogen, or hexone bases nitrogen, which is precipitated by phos-
photungstic acid as basic products (to which also the guanidine residue
of arginine belongs); (4) monamino-acid nitrogen; and (5) the nitrogen
1
See " Eiweisskorper," Ladenburg’s Handworterbuch der Chemie, 3, 534-589,
which gives a complete summary of the literature of protein substances up to 1885.
The more recent literature may be found in O. Cohnheim, Chemie der Eiweisskorper,
Braunschweig, 1911. See also Oppenheimer’s Handbuch der Biochem. der Menschen.
und der Tiere, 1908.
77
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