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 108), 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 HN0 2 (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, Zeitschr. f. physiol. Chem., 27 and 29; Henderson, 

 ibid., 27; Kossel and Kutscher, ibid., 30; Kutscher, ibid., 31, 38; Hart, ibid., 33; 

 Giimbel, Hofmeister's Beitrage, 5; Rothera, ibid. 



2 See the works given in footnote 1 and Blum, Zeitschr. f. physiol. Chem., 30; 

 Kossel, Ber. 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 and 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. 



