NITROGEN DISTRIBUTION. 79 



By the action of nitrous acid upon proteins at least a partial deamidation 

 takes place and so-called desamino proteins are obtained. The nitrogen expelled 

 originated from the NH 2 groups according to the formula RNH 2 +HN0 2 = ROH-j- 

 N 2 +H 2 0. The amount of such nitrogen is generally only small, 1-2 per cent, 

 and for this reason it has been accepted that such groups only occur in small 

 amounts in the proteins. This is probably true for a large number of proteins 

 but not for all and as example of these we will recall that KOSSEL and CAMERON 1 

 have shown that those protamiries which contain no other hexone base besides 

 arginine although they have NH 2 groups at the ends in the guanidine residue 

 HN.CNH.NH 2 of the numerous arginine groups, do not yield any nitrogen on 

 using v. SLYKE'S method while those protamines containing lysine do. We must 

 be very careful in drawing certain conclusions from the results obtained by the 

 action of nitrous acid upon proteins. 



The nitrous acid can develop nitrogen from the NH 2 groups of the acid amides 

 as well as from the NH 2 groups of the amino-acids. On the contrary no nitrogen 

 is evolved in v. SLYKE'S method from the guanidin groups and from the peptid 

 combinations containing imid groups (see below). This is also the reason, as 

 remarked above, why those protamines containing only arginine do not yield 

 any nitrogen while those protamines which also contain lysine where there exist 

 free NH 2 groups do give off nitrogen. On hydrolyzing these deamidized pro- 

 tamines and also other deamidized proteins we therefore do not obtain any lysin 

 as shown by SKRAUP and collaborators and by LEVITES for certain proteins. 

 The quantity of monamino-acid nitrogen is therefore in such cases found to be 

 increased. 



According to OSBORNE, LEAVENWORTH and BRAUTLECHT, 2 who worked 

 with plant proteins, the splitting off of NH 3 on the acid hydrolysis of the proteins 

 was very similar to the splitting off of NH 3 from the acid amide asparagine, so 

 that the binding of NH 2 groups on the carboxyl groups seems very probable. 

 The quantity of NH 3 split off in the hydrolysis ran parallel with the amount 

 of asparagine and glutamic acid present and the quantity of NH 3 , split off by 

 hydrolysis with alkali corresponded nearly to the sum of the ammonia that was 

 split off by acid hydrolysis and one-half of the arginine nitrogen. According to 

 these investigators the NH 2 groups occur chiefly as acid-amide combinations. 



A part of the nitrogen in the proteins occurs from the above, undoubt- 

 edly as NH2 groups; the extent of this part, which is different in different 

 proteins cannot be positively given. The chief mass of the nitrogen 

 in the proteins, although other forms of binding occur, exists as imide- 

 like combinations of amino-acids united together and this will be com- 

 pletely developed in the following pages. 



The sulphur occurs in the different proteins in very different amounts. 

 Certain of them, such as the protamines and apparently also certain 



1 In regard to the action of nitrous acid upon proteins, their deamidation and cleav- 

 age products see C. Paal, Ber. d. d. Chem. Gesellsch., 29; H. Schiff, ibid., 1354; O. 

 Loew, Chemiker Ztg., 1896 and O. Nasse, Pfluger's Arch., 6; Treves and Salomone, 

 Bioch. Zeitschr, 7; Skraup, Monatsh. f. Chem., 27 and 28, with Hoernes, ibid., 27, 

 with Kaas, Annal. d. Chem. u. Pharm., 351; Lampel, Monatsh. f. Chem., 28; Traxl, 

 ibid., 29; Levites, Zeitschr. f. physiol. Chem., 43, and Bioch. Zeitschr., 20; D. v. 

 Slyke, foot-note 4, page 78; Kossel and Cameron, Zeitechr. f. physiol. Chem., 76; Kossel 

 and F. Weiss, ibid., 78. 



2 Amer. Journ. of Physiol., 23. 



