78 THE PROTEIN SUBSTANCES 



tion does not have sufficient foundation, for, according to LEVITES,* 

 the quantity of amide nitrogen is not diminished by the action of nitrous 

 acid upon the protein substances. SKRAUP and co-workers have in part 

 obtained similar results, and the deamidized proteins, the desamidoprotein 

 at least in certain cases, do not strikingly differ in elementary composi- 

 tion from the original mother-substance. The so-called deamidation 

 of proteins seems to be a rather complicated process whose nature is 

 not well understood, 2 and therefore no positive conclusions can be drawn. 



If by the action of HN0 2 only acid amide groups are attacked, then we should 

 expect that the corresponding deamidized protein would yield on hydrolysis 

 the same amino acids as the mother substance. If, on the contrary, the nitrous 

 acid reacts also with NH 2 groups of the amino acids with an exchange of OH 

 for NH 2 , then it is apparent that on the hydrolysis of the diamino protein we 

 would find other cleavage products, namely, oxyacids instead of amino acids, 

 and either oxyacids or oxyamino acids instead of diamino acids. By the absence 

 of certain cleavage products and the occurrence of others, we can with probability 

 determine which of the cleavage products were so combined that one or the 

 other NH 2 groups was free. From this standpoint SKRAUP and his co-workers 

 have studied the hydrolytic cleavage products of the diamino proteins, and have 

 found that these products, with the exception of lysin and in certain cases, A part 

 of the arginine, were the same qualitatively and quantitatively as from the mother 

 substance. Nearly all amino acids occur, it seems, in the investigated proteins 

 in a form of binding when the amino groups are not free. 



The chief part of the nitrogen in the proteins exists as an imide-like 

 binding of the amino-acids, but other forms of bondage may occur at the 

 same time. This will be 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 

 bacterial proteids, 3 are free from sulphur; some, such as gelatin and 

 elastin, are very poor in sulphur, while others, especially horn sub- 

 stances, are relatively rich in sulphur. On hydrolytic cleavage with 

 mineral acids, the bulphur of the protein substances is regularly, at least 

 in part, split off as cystine (K. MORNER) or, with bodies poorer in sul- 

 phur, as cystein (EMBDEN), but this, according to MORNER and PATTEN, 

 is a secondary formation. From certain protein substances a-thiolactic 

 acid (SUTER, FRIEDMANN, FRANKEL), which MORNER claims is also pro- 

 duced secondarily mercaptans and sulphuretted hydrogen (SIEBER and 



1 Levites, Zeitschr. f . physiol. Chem., 43. 



2 On the deamidation of proteins and their cleavage products see footnote 5, page 

 77; Treves and Salomone, Biochem. 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. 



3 See Nencki and Schaffer, Journ. f . prakt. Chem. (N. F.), 20, and M. Nencki, Ber. 

 d. d. chem. Gesellsch., 17. 



