抄録
1. Two methods, called the bromine method and iodine method, for the determination of cysteine are described.
2. The principle of the bromine-method is to titrate cysteine with a bromate solution in the presence of acid and bromide. A single determination of cysteine by this method requires only a few minutes, but it can not be used in the presence of some amino acids such as cystine, tyrosine and tryptophane.
3. The principle of the iodine-method is to titrate cysteine in a hydrochloric acid solution, in the presence of iodide, with a standard iodate solution. The procedure of this method is not so simple as that of the bromine-method, but the method is applicable in the presence of all the cleavage products of proteins. Consequently it is available for the qualitative and quantitative determination of cysteine in amino acids mixture.
4. It was proved that to oxidize one molecule of cysteine to cysteic acid 6 atoms of bromine are required.
