POTENTIOMETRIC DETERMINATION OF CYSTINE AND CYSTEINE
1930 Volume 12 Issue 2 Pages 207-222
Details
1930 Volume 12 Issue 2 Pages 207-222
It is recommended to apply the potentiometric titration for the determination of cystine and cysteine, the details of which are reported in this paper. Here the following jsummary is given.
1. Pure cystine and cysteine solution can be accurately titrated with broinate either in the presence of bromide or in its absence.
2. If the solution contains other aminoacids besides cystine, such as protein hydrolysate the titration with iodate in the presence of iodine is more accurate.
3. As is already depicted by Okuda, the temperature and the acidity of the solution have the marked. effects upon the the titrating value, because cysteine can be oxidised to cystine or crysteinic acid in varying ratio as these factors change.
4. It was found, moreover, that the rate of titration with iodine has also some influence. When it is carried out more slowly the more cystine is formed and in the reverse case the more cysteinic acid.
5. Among various aminoacids only tryptophan exerts a definite influence upon the titrating value of cysteine by iodate. Perhaps the oxidation of tryptophan may be induced by the presence of cysteine.
The author is deeply indebted to Prof. Keizo Kodama for his kind advice throughout this investigation.
