Specific Rotation of Cystine Excreted in Cystinuria

The identity of stone cystine and protein cystine has been generally accepted in recent years. Gortner and Hoffman in an examination of cystine isolated from kidney calculi observed a specific rotation at 20° in 0.1 N hydrochloric acid of —242.6°, a figure much higher than any value recorded in the literature for either stone or protein cystine. They believe that the conflicting observations make necessary the conclusion “that cystine is an extremely labile compound and possibly occurs in more than one form so that persons working with cystine are probably working with a mixture of substances and that this mixture varies in composition depending at least upon (1) the source of the biological material from which the cystine is prepared, and (2) the method of preparation which is used for the isolation and purification of the amino acid.” The different values for specific rotations of cystine recorded in the literature can in all probability be explained by varying degrees of racemization or by failure to use standard conditions for the determination of the specific rotation,, but it remains to be demonstrated that the optical properties of cystine vary with the biological source of the amino acid. In studies with a cystinuric patient we observed that crystals, which were observed to be almost pure cystine on microscopic examination, separated very rapidly after the sample was collected. Since the pH of the urine was 6.8 to 7.2, an opportunity was afforded to determine the specific rotation of the cystine excreted in cystinuria, a cystine which had not been subjected to high concentrations of acid or alkali and which should show minimal racemization.