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78 THE PROTEIN SUBSTANCES.
in variable amounts which appears as humus-like melanoidins, which
seem to be of only secondary formation as products of elaboration.
The quantitative division of the total nitrogen between the above
five groups is different in the various protein substances, and more-
over cannot be given with certainty, because of the above-mentioned
melanoidin formation and the errors in the methods used.1
The follow-
ing gives at least an approximate idea of this division.2
The loosely
combined so-called amide nitrogen seems to be entirely absent in the
protamines. In the gelatins we find 1-2 per cent, and 5-10 per cent
in other animal protein substances,3
in certain plant proteins, the
prolamines (see page 106), 13-25 per cent of the total nitrogen is amide
nitrogen. The guanidine nitrogen may amount in the protamines to
22-44 per cent of the total nitrogen, in the histones to 12-13 per cent,
in the gelatins about 8 per cent, and in the other protein bodies about
2-5 per cent. As basic nitrogen precipitable by phosphotungstic acid
(including the guanidine residue) we find 35-88 per cent in the protamines,
35-42.5 per cent in the histones, 15-30 per cent in the other animal pro-
tein substances. In the prolamines 3-6 per cent of the total nitrogen is
found as products precipitable by phosphotungstic acid but in plant
globulin (globulin of the wheat) indeed 37 per cent. The chief quantity
of the nitrogen, 55-76 per cent, occurs, with the exception of the pro-
tamines, as the monamino-acid groups. The results for the melanoidin
nitrogen vary so considerably that they will not be mentioned.
Recently D. v. Slyke 4
has perfected a method which is based upon "the
deamidation of the amino-acids by HN02 (see below) and which allows of a still
more detailed differentiation of the nitrogen partition. In this method the
nitrogen of the ammonia, the melanines, the cystine, arginine, histidine, proline and
oxyproline besides one-half of the tryphtophane nitrogen as well as the nitrogen
of the remaining amino-acids can be specially determined.
From recent as well as older observations it follows as chief result
that the nitrogen in the proteins occurs in such combinations so that
on hydrolysis with acids, its chief amount splits off in the form of amino-
acids.
1
See the work of Hausmann, Zeitsehr. f. physiol. Chem., 27 and 29; Henderson,
ibid., 27; Kossel and Kutscher, ibid., 30; Kutscher, ibid., 31, 38; Hart, ibid., 33
Giimbel, Hofmeister’s Beitriige, 5; Rothera, ibid.
2
See the works given in footnote 1 and Blum, Zeitsehr. f. physiol. Chem., 30
Kossel, Her. d. d. chem. Gesellsch., 34, 3214; Hofmeister, Ergebnisse der Physiol.
Jahrg. I, Abt. 1, 759, which also contains the literature; Osborne and Harris, Journ
Amer. Chem. Soc, 25; and Giimbel, I.e.
3
Skraup and v. Hardt-Stremayr, Monatsh. f. Chem., 29, found lower results than
other investigators arid they found also that about two-thirds of the amide nitrogen
was readily split off and one-third slowly.
4
Ber. d. d. chem. Gesellsch, 43 and 44 and Journ. of biol. Chem., 9, 10 and 12.
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