vii OXIDATION-PRODUCTS 245 



non-nitrogenous substances as lactic acid and tartaric acid by means 

 of strongly ammoniacal permanganate solutions, Hofmeister l and 

 Halsey " 2 have shown, but on the other hand there cannot be any doubt 3 

 that urea is formed directly from albumin, especially in the light of 

 Kutscher and Zickgraf's discovery of guanidin amongst the products of 

 oxidation, and Kossel and Dakin's urea-forming arginase (see index), 

 and this ' direct ' urea, although it only amounts to 10 per cent of the 

 total urea excreted, 4 must be accounted for, and therefore Kutscher, 

 helped by Schenck, Zickgraf, and especially Seeman, has made a 

 number of investigations into the structure of the albumin-molecule by 

 means of graduated oxidation. 



If we assume with Kossel that an albumin-molecule possesses a 

 central region or protamin-nucleus, round which the other amino-acids 

 are arranged according to Hofmeister's conception (see p. 139), and if 

 the biuret-reaction depends on the special way in which the arginin- 

 radicals of the protamin are linked together, 5 then the disappearance of 

 the biuret-reaction should coincide with the maximal yield of guanidin, 

 which latter is derived from arginin. Zickgraf 6 has now actually found 

 by treating the same amounts of boiling gelatine-solution with increasing 

 amounts of calcium-permanganate solution that the maximal amount of 

 guan id in-pi crate is obtained at the time when the biuret-reaction gives 

 negative results. Seemann 7 derives the larger amount of oxalic, 

 succinic, and formic acids found amongst the oxidation-products, from 

 radicals lying in proximity to the protamin-nucleus, because these 

 readily oxidisable acids occurred in relatively large amounts, notwith- 

 standing that the oxidation of gelatine had been carried very far, 

 though not to the disappearance of the biuret-reaction. Seemann 

 derives the oxalic acid from amino- chains according to the following 

 plan : 8 



CH 3 (CH^ CH . CO . NH K 



COOH (CH 2 ) X H + NH 3 + COOH . CO . NH R 



or -> C0 2 + (CO^ + NH 3 + COOH . CO . NH R 



1 F. Hofmeister, Arch. f. experim. PatJiol. u. Pharm. 37. 436. 



2 Halsey, Zeitschr. f. physiol. Chem. 25. 329 (1898). 



3 J. Seemauu, ibid. 44. 238 (1905). 



4 Drechsel, Ber. d. deutsch. chem. Ges. 33. 3101 ; Gulewitsch, Zeitschr. f. physiol. 

 Chem. 30. 526 and 532 (1900). 



5 Arginin itself does not give the biuret-reaction. 



6 G. Zickgraf, Zeitsch. f. physiol. Chem. 41. 259 (1904). 



7 J. Seemann, ibid. 44. 229 (1905). 



8 Compare with Ehrmann's vieAv on p. 243. 



