CYSTINE. 147 



and at the present time we cannot admit of the occurrence of two different 

 cystines. 



Cystine probably occurs normally as traces in the urine. In rare 

 cases, in cystinuria, it occurs in larger quantities in the urine sediment 

 or in calculi. Traces have also been found in the ox-kidney, in the liver 

 of the horse and dolphin, and in the liver of a drunkard. ABDER- 

 HALDEN 1 has found cystine in the urine and also abundantly in the 

 organs (spleen) in a case of parental cystine diathesis. 



The constitution of cystine has been explained by FmEDMANN, 2 and 

 he has also established the relation between cystine and taurine. 

 Cystine is the disulphide of cysteine, which is a-amino-/?-thiolactic acid. 

 From cysteine by oxidation FRIEDMANN obtained cysteinic acid, 



CH 2 SO 2 OH 

 C 3 H 7 NSO5 = CH(NH2), from which taurine CH 2 (SO 2 OH) is produced by 



COOH CH 2 (NH 2 ) 



splitting off C0 2 . 



a-Cystine has also been prepared synthetically. Starting from formyl 

 hippurate, ERLENMEYER, JR. and STOOP first prepared the benzoylserine 

 ester, and then with phosphorus pentasulphide they obtained the 

 benzoylcystine ester. On splitting the latter with HC1 they obtained 

 cysteine, and then on oxidation inactive cystine. GABRIEL has also 

 prepared an isocysteine by the cleavage of sulphocyanatedihydrouracil 

 with hydrochloric acid, and then inactive cystine by the oxidation of this 

 isocysteine, and recently FISCHER and RASKE S have prepared cystine 

 from a-amino-/?-chlorpropionic acid (obtained from Z-serine) by the 

 action of barium hydrosulphide and a subsequent oxidation in the air. 



l-a-Cystme crystallizes in thin, colorless, hexagonal plates. It is not 

 soluble in water, alcohol, ether, or acetic acid, but dissolves in mineral 

 acids and oxalic acid. It is also soluble in alkalies and ammonia, but not 

 in ammonium carbonate. Cystine is optically active, being levorotatory. 

 MORNER found it to be (a) D = 224.3. On heating with hydrochloric 

 acid it can, according to MORNER, be changed into a modification crys- 

 tallizing in needles and with a weaker levorotatory power, or indeed 

 dextrorotatory, composed of a mixture of the two optically active 

 cystines. On heating with HC1 to 165 for 12-15 hours NEUBERG and 

 MAYER obtained inactive cystine. By fungus fermentation with Asper- 

 gillus niger they obtained dextrorotatory cystine. Cystine has no melt- 

 ing-point but slowly decomposes at 258-261. On boiling cystine with 



1 Zeitschr. f. physiol. Chem., 38. 



2 Hofmeister's Beitrage, 3. 



3 Erlenmeyer and Stoop, Ber. d. d. chem. Gesellsch., 36; Gabriel, ibid., 38; Fischer 

 and Raske, ibid., 41. 



