60 THE GENERAL CHARACTERS OF THE PROTEINS 



There is not sufficient experimental material to draw any very 

 definite conclusions as to the course of oxidation of the proteins, but 

 some suggestions of Hofmeister seem reasonable. If the typical 

 polypeptide grouping of a protein be represented as follows 

 NH CH . CO NH . CH CO 



k J- 



the first stage of the oxidation would be 



NH CH CO NH . CH CO- 

 COOn COOH 



from which, by CO 2 scission, the grouping 



NH CH 2 . CO NH . CH 2 . CO 



would be formed, which on further oxidation would yield a group 



NH . CO . CO NH . CO . CO 



From such a group, by hydrolysis, oxalic acid and ammonia would 

 be obtainable. It is of interest to note that Zickgraf, Seemann, and 

 Kutscher and Schenck have obtained by the oxidation of proteins 

 oxaluramide 



CO NH X 



I >CO 



CO.NH 2 NH 2 / 



which contains the complex NH CO CO NH 



The hypothesis is, however, insufficient to explain all the facts 

 connected with the oxidation, as the amount of amide nitrogen, 

 which can be eliminated with nitrous acid, does not correspond with 

 the amount of oxalic acid. 



Oxidation with Hydrogen Peroxide and Ozone. 



The oxidation of proteins by hydrogen peroxide has been studied 

 by Wurster and by F. N. Schulz, and the action of ozone has been 

 studied by v. Gorup-Besanez and Harries and his pupils. Wurster 

 and Schulz noticed that egg-albumin (Wurster used egg-white solu- 

 tion and Schulz the crystallised product) on standing with excess of 

 hydrogen peroxide in neutral solution at 37 C. deposited after a 

 time the protein in an insoluble form. The product thus obtained 

 was subjected to a detailed examination by Schulz, who found that 

 it did not differ very greatly from the original protein in its per- 

 centage composition. The ratio of hydrogen, carbon and nitrogen 

 was practically unchanged, but it contained about 2*6 per cent, more 

 oxygen. Schulz designated this substance oxyprotein, and he showed 

 that, unlike the oxyproteic acids, it yielded the ordinary protein re- 

 actions. It represents, therefore, a simple oxidation product. 



Blumenthal and Neuberg have shown that gelatin, in the pre- 

 sence of an iron or copper salt, yields, on oxidation with hydrogen 

 peroxide, acetone. The same product has been obtained by Orgler 

 from egg-albumin, using the same method. 



The action of ozone on caseinogen has recently formed the sub- 

 ject of an extensive research by Harries and Langheld. By pro- 

 longed action of ozone on the sodium salt considerable chemical 

 change took place. A product was obtained which gave a marked 

 biuret reaction, but no reaction with the xanthoproteic, Millon or 

 Hopkins reagents (cf. oxyproteic acids). It gave a precipitate with 



