Amino-acids.V. 105solutions of casein-hydrochloric acid, and reckoning back to concentrations of these two ions after the activity theory, it was found that the casein in the solution binds per g (not dried) about 2.10 gram equivalents of chlorine ions, and dissociation degree of casein chloride is about 0.72. It will be also noted that the dissociation degree of casein chloride and the number of complex-bound gram-equivalents of chlorine ions per g casein, appear to be independent of the hydrogen ion activities used. (June 18, 1925.) On Sulphur-containiny Amino-acids. VOn the Oxidation of Cystine and Cysteine by Iodine.by YUZURU OKUDA and MUNEKUMA SAMEJIMA.From the biochemical Laboratory, Department of Agriculture, Kyushu Imperial University, Fukuoka, Japan.Friedmann (Beitr. Chem. Physiol. Pathol., 3, 1. 1902) has found that cystine as well as cysteine are oxidized by bromine into cysteic acid, and Okuda (J. Tokyo Chem. Soc., 37, 181, 1916, and J. Chem. Soc. Japan, 45, 1, 1924.) studied this oxidation quantitatively, and ascertained that in these cases one molecule of cystine requires 10 atoms of bromine and one molecule of cysteine 6 atoms, and applied these facts for the determination of them.Lately, Okuda (J. Chem. Soc. Japan, 45, 1, 1924 and 19, 1924.) also found that among amino acids cysteine alone reacts with iodine very actively in an acid solution and at room temperature, and applied this fact for the determination of cystine and cysteine. But on the oxidation products in this case no further investigation was performed.In the present investigation the following facts were ascertained:-1. At At higher temperature both cystine and cysteine are oxidized into cysteic acid, one molecule of cystine requiring 10 atoms of iodine and one molecule of cysteine 6 atoms of iodine for oxidation. 2. At room temperature and in hydrochloric acid solutine, cystine does not react with iodine. But cysteine does, and the chief oxidation product is cystine, accompanyed by a little cysteic acid. The ratio of the quantities of the oxydation products depends upon the acidity and temperature of the sample.
The purpose of this investigation was to make some quantitative studies concerning the presence of cysteine group in the protein molecule, a subject on which, as far as we know, no work has hitherto been done.
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