GENERAL CHEMICAL CHARACTERS OF PROTEINS 59 



Nevertheless several investigations on the direct oxidation of 

 proteins without previous hydrolysis deserve mention. 



Oxidation with Permanganate. 



The oxidation with permanganate solution has been the subject 

 of repeated studies. 1 The chief investigations are due to Maly and 

 von Furth. Other investigators were Be*champ, Sabbotin, Pott, 

 Briicke, Chandelon, Low, Siegfried, Bondzynski and Zoja, Bernert 

 and Ehrmann. 



Maly, under the name of oxyprotosulphonic acid, described a pro- 

 duct which he obtained by oxidising egg-white with half its weight 

 of potassium permanganate in the cold. Under the name of peroxy- 

 proteic acid he described a product which was obtained by slowly 

 adding small portions of permanganate to a protein solution, at room 

 temperature, until only very slow oxidation took place. This acid, 

 isolated by precipitation with salts of heavy metals (mercury, 

 lead, etc.), gave a marked biuret reaction, but was not precipitated 

 by the ordinary alkaloidal reagents. On gentle treatment with 

 baryta water a large amount of ammonia was evolved, and separation 

 of oxalic acid in the form of its barium salt took place. By con- 

 tinued hydrolysis with baryta, lasting for several days, glutamic acid, 

 leucine, formic, acetic and ben zoic acids were obtained. 



Further investigations on the oxyprotosulphonic acid from egg- 

 white were carried out by Bernert and Ehrmann. 



The most complete of the recent investigations on the perman- 

 ganate oxidation products are due to von Furth. He oxidised 

 caseinogen with four times its weight of potassium permanganate at 

 room temperature, the reaction taking several weeks to complete. 

 A product was obtained which was resistant to further action of the 

 oxidising reagent. This was shown to consist of at least three pro- 

 ducts of high molecular weight, which gave the biuret reaction, but 

 not the Millon, xanthoproteic or Hopkins reactions, and which 

 could be separated by fractional precipitation with silver nitrate 

 (A), lead acetate (B), and mercuric acetate (C). From the three 

 peroxyproteic acids thus obtained, the esters could be readily pre- 

 pared by means of alcoholic hydrochloric acid. On treating these 

 acids with barium hydroxide a scission took place of oxalic acid, in 

 the form of its barium salt ; there was also a considerable loss of 

 nitrogen. The substances obtained in this way were designated by 

 von Furth as desamino-proteic acids, and they yielded on hydrolysis 

 glutamic acid, leucine, benzoic acid and ammonia. Unlike the 

 oxyproteic acids, from which they were derived, they were no longer 

 resistant to further oxidation with permanganate ; the scission of the 

 oxalic groups had left a new position of weakness in the molecule, 

 and the desamino-acids readily oxidised on further addition of the 

 oxidising agent, yielding a mixture of substances of a new class 

 called the kyroproteic acids, which gave a marked biuret reaction. 

 By means of lead acetate, these could be separated into acids which 

 contain a large quantity of oxygen, which could be readily oxidised 

 further. The kyroproteic acids, furthermore, on treatment with nitrous 

 acid, readily lose half their nitrogen, relatively five times as much as is 

 lost by caseinogen by similar treatment. 



*A succinct account of the earlier literature is given in von Fiirth's paper, 1905. 



