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138 THE PROTEIN SUBSTANCES.
typical protein. The occurrence of basic protokyrins in the hydrolytic
cleavage of genuine proteins like gelatin has given valuable support to
Kossel’s theory as to a basic nucleus in the protein bodies.
On account of the cleavage taking place in digestion, the digestive
products should have a lower molecular weight than the original protein.
This is really the case as shown by molecular weight determinations.
As these determinations have been made upon impure substances or
mixtures, the results 1
obtained are only of little value. The same is
true for the elementary analysis of the proteoses and peptones.2
v —
In the preparation and separation of various proteoses and peptones
all precipitable protein is always removed first by neutralization and
then by boiling. The proteoses may then be separated from the pep-
tones by means of ammonium sulphate according to Ivuhne’s method,
and divided into different fractions according to the method of Pick
and the Hofmeister school. The separation and preparation of pure
hetero- and protoproteoses can be best performed by the method sug-
gested by Pick, but this method, as well as that with ammonium sulphate,
gives good results only when the precautions suggested by Haslam 3
are carefully followed. We can here only refer to the cited works of
Kuhne and co-workers, of E. Zunz and especially those of the Hof-
meister and the Siegfried schools. In regard to the literature on the
detection of proteoses and peptones in animal fluids we refer to Chapters
V and XIV.
If we wish to detect the presence of so-called true peptone, by means
of the biuret reaction in a solution saturated with ammonium sulphate,
we add a slight excess of a concentrated solution of caustic soda and
cool, and then add a two per cent solution of copper sulphate drop by
drop, after the sodium sulphate has separated out.
In the quantitative estimation of proteoses and peptones we make
use of the nitrogen estimation, the biuret test (colorimetric), and the
polarization method. These methods do not give exact results.
The polypeptides have had their most important properties dis-
cussed on pages 85-91, and of the cleavage products of the proteins only
the amino-acids remain to be discussed.
1
Sabanejew, Ber. d. d. chem. Gesellsch., 26, 385; Paal, ibid., 27, 1827; Sjoqvist,
Skand. Arch. f. Physiol., 5.
- Klernentary analyses of proteoses and peptones will be found in the works of
Kuhne and Chittenden and their pupils, cited in footnote 2, p. 130; also by Herth,
Zeitschr. f. physiol. Chem., 1, and Monatshefte f. Chem., 5; Maly, Pfluger’s Arch.
9, 20; Henninger, Compt. rend., 86; Schrotter, 1. c, Paal, 1. c.
3
Journ. of Physiol., 32 and 36.
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