Cystine Metabolism 



361 



wished to investigate the reactions by which cystine is apparently 

 converted into cystein, and cystein into cystine in the body. 



4. In studying the catabolism of cystine we decided to deter- 

 mine, if possible, the origin of the ethereal sulfates. 



Lewis 3 has found that the sulfur of phenyluramino cystine 

 is not to any great extent oxidized. He has shown that the com- 

 pound is however apparently split into phenyluramino cystein, 

 as he obtains a decided test with sodium nitroprusside, and ferric 

 chloride, on the urine of rabbits after feeding the phenyluramino 

 cystine. 



Schmidt 4 has shown that taurine, CH ■ NH 2 • CH 2 ■ S0 3 H, is 

 not catabolized in the body but passes out in the urine unchanged. 

 Cysteic acid, C0 2 ' HCH ■ NH ■ CH 2 ■ S0 3 H, only undergoes hy- 

 drolytic deamination but not oxidation in the body. 



We have fed to rabbits phenylacetyl cystine, phenyluramino 

 cystine, phenylhydantoin cystine as well as cystine itself. 



In these derivatives of cystine either the amino group alone 

 or the amino and carboxyl group were both blocked, and our 

 results have shown that a protecting of the amino group does 

 not seem to entirely protect the sulfur, as considerable of it is 

 excreted as sulfates. 



We fed on each of three succeeding days phenylacetyl cystine 

 to one rabbit and phenyluramino cystine to another rabbit in 

 such amounts that each rabbit received 0.4 grams sulfur. Only 

 a small amount of the phenylacetyl cystine could be traced, as 

 most of it was completely lost. Enough of the original sub- 

 stance was recovered and isolated to determine the melting point 

 and also some of it was reduced to the corresponding cystein 

 compound as shown by the sodium nitroprusside test, but at- 

 tempts to convert this phenylacetyl cystine into benzylpheny- 

 lacetyl cystein, for its further identificaion were impossible. 



In the case of the phenyluramino cystein, we were able not 

 only to isolate some of the substance fed, but proved the pres- 

 ence of the corresponding cystein compound by extracting it 

 from the urine and converting it into the benzyl derivative which 



3Lewis, H. B., and Eoot, L. E., J. Biol. Chem., 1922, 1, 303 ; Lewis, H. B., 

 and McGinty, D. A., Ibid, 1922, liii, 349. 



4 Schmidt, C. L. A., Adelung, Von Aldelung, E., and Watson, T., J. Biol. 

 Chem., 1918, xxiii, 501; Schmidt, and Allen, E. G., Ibid, 1920, xlii, 55; 

 Schmidt, and Clark, G. W., Ibid, 1922, liii, 193. 



