OXYPROTEIC ACIDS. 755 



LIEBERMANN * this acid is not a unit substance, and contains a part of 

 its sulphur as ethereal sulphuric acid, and it also contains uroferric acid. 



The urochrome, which has been specially studied by DoMBROWSKi, 2 is con- 

 sidered by him and BONDZYNSKI as belonging to the oxyproteic acid ' group. I 

 contains about 5 per cent sulphur, is precipitated by copper acetate and yields 

 melanin-like substances on its decomposition. No positive proofs are at hand in 

 regard to the purity of this urochrome and the reports as to its composition, 

 which are very contradictory, do not exclude the possibility that this is a mixture 

 of a yellow pigment with another substance (see page 741). 



BROWINSKI and DOMBROWSKI 3 have carried out investigations on the nitrogen 

 titratable with formol on the oxyproteic acids before and after acid hydrolysis. 

 They found that the antoxyproteic acid and the oxyproteic acid did not contain 

 any nitrogen split off as NH 3 by MgO before hydrolysis, while the alloxyproteic 

 acid as well as the urochrome yielded about 3 per cent of the total nitrogen in this 

 form. After acid hydrolysis all gave about the same quantity of ammonia. The 

 two first-mentioned acids, especially oxyproteic acid, were before hydrolysis 

 considerably richer in amino groups, titratable with formol, than the others. 

 This indicates that these two acids are produced from the proteins by a deeper 

 cleavage than is the alloxyproteic acid. The large amount of free amino groups, 

 which occur especially in the oxyproteic acid and which amount to 38.8 per cent 

 of the total nitrogen, is nevertheless remarkable. 



The preparation of the three above-mentioned acids is based in part 

 upon the fact that alloxyproteic acid alone is precipitated by basic lead 

 acetate and that the two other acids can be precipitated from the ni- 

 trate by mercuric acetate, the antoxyproteic acid in acetic acid solution 

 and the oxyproteic acid in neutral solution. The preparation is never- 

 theless very tedious and complicated and therefore we must refer to the 

 original works for details. 



Uroferric acid is an acid isolated by THIELE 4 from the urine, according to 

 SIEGFRIED'S method for preparing pure peptone. It also contains sulphur, 3.46 

 per cent, and has the formula CasHseNsSOig. The acid forms a white powder 

 which is readily soluble in water, saturated ammonium-sulphate solution, and 

 methyl alcohol. It is soluble with difficulty in absolute alcohol, insoluble in benzene, 

 chloroform, ether, and acetic ether. About one-half of the sulphur can be split 

 off as sulphuric acid on boiling with hydrochloric acid. The acid gives neither 

 the biuret test nor MILLON'S or ADAMKIEWICZ'S reactions. It is precipitated by 

 mercuric nitrate and sulphate, and also by phosphotungstic acid. This acid is 

 hexabasic, and its specific rotation at 18 C. (QJ)D = 32.5. On cleavage it 

 yields melanine substances, sulphuric acid, aspartic acid, but no hexone bases. 

 The existence of this acid is disputed by BONDZYNSKI, DOMBROWSKI and PANEK. 

 The investigations of GINSBERG also contradict the occurrence of such an acid, 

 because no sulphuric acid could be split off from the mixture of the oxyproteic 

 acids by hydrolysis. 



Methods for the quantitative estimation of the total oxyproteic 

 acids have been suggested by GINSBERG and by GAWINSKI. S Accord- 



1 Zeitschr. f. physiol. Chem., 52. 



2 Ibid., 46 and 62. 



3 Ibid., 77. 



4 Zeitschr. f. physiol. Chem., 37. 



8 Ginsberg, Hofmeister's Beitrage, 10; Gawinski, Zeitschr. f. physiol. Chem., 58. 



