104 THE CHEMICAL CONSTITUTION OF THE PROTEINS 



Cystine. 



This compound was first described by Wollaston in iSiounder 

 the name of cystic oxide, and was obtained from a urinary calculus. 

 Lassaigne found it under the same conditions in a dog in 1823. Its 

 presence in the kidney of an ox was shown by Cloetta in 1856, and in 

 the following year Scherer found it in the liver of a patient, who had 

 died from typhoid fever. The name cystine was given to it by Berzelius. 

 Drechsel, in 1891, isolated it from horse's liver and in 1896 from a 

 porpoise, and first regarded it as a normal product of metabolism. 

 Arnold finds that cysteine, the reduction product of cystine, is present 

 in all animal organs. In 1 890 Kiilz obtained cystine by the digestion 

 of fibrin with pancreas, and Emmerling, in 1894, found it mixed with 

 tyrosine which he had prepared by the hydrolysis of horn. An attempt 

 was made by Suter, in 1895, to obtain it from horn, but he could only 

 obtain a-thiolactic acid, and it was not until 1899 that it was shown 

 by K. A. H. Morner to be a product of hydrolysis of this protein, and 

 in 1901 also of other proteins. His results were confirmed by 

 Embden, who was working independently and also obtained cysteine, 

 which, as proved by Patten, is derived from cystine. 



The earliest analyses of cystine are given by Prout, who overlooked 

 the fact that cystine contained sulphur, the presence of which element 

 was first shown by Baudrimont and Malagutis. Thaulow gave cystine 

 the formula C 6 H 12 N 2 O 4 S, and pointed out that it was one of the few 

 compounds made up of five elements. On account of the uneven 

 number of atoms in its molecule, Gmelin replaced this formula by 

 C 3 H 7 NSO 2 , which formula was confirmed by Grote in 1864, and later 

 by Kiilz in 1884. 



The first investigations on the constitution of cystine are those of 

 Dewar and Gamgee in 1871, who, on treating cystine with nitrous 

 acid, obtained an acid which they thought was pyruvic acid, 

 CH 3 .CO.COOH, and on this account gave cystine the constitu- 

 tion of 



CH 2 (H 2 N) 



CS or C 3 H 6 NSO, 



COOH 



Hoppe-Seyler, as cited by Baumann and Preusse, showed that the 

 nitrogen of cystine was separated off by alkalies as ammonia and not 

 as methylamine, as would be expected from this formula, and he more- 

 over maintained that the formula was C 3 H 7 NSO 2 . 



