New Method For The Determination of Cystine and Cysteine, and Their Application

Abstract

From this equation we know that -, molecule ('07.92 g) of potassium bromate corresponds to 0 atoms (479.5 g.) of bromine, or 4-4 C.c. of Mj20 KBr0 3 to 0.'053 g. of bromine.And 0034 g. of cysteine hydrochloride contains 0.020' g. of cysteine.Consequently one molecule of cysteine (Ln. '4 g.) corresponds to 488.7 g.(about 6 atoms) of bromine. 12 I. 14 x 0.1053/0.0261 = 488.7 (b). 0.034 g. of cysteine hydro~hlorid~ was dissolveu in 20 C.C. of 10 per cent hydrochloric acid and th~n titrated with 0 33 per cent bromine water. It requircd 30.8 C.c. of the solution, which correspollus to 0.1016 g. of bromine. Therefore the result falls into line with that of experiment (a), namely one molecule of cysteine corresponds to 0 atoms of bromine. From the results of these two' experi~lents we migl1t assume the following equation to express the relation between cysteine and bromine. CH 2 -SH CH 2 -S0 3 H CH-NH2 + 6Br + 3H20 COOH CH-NH2 + 6HBr COOH (c). For the purpose of ascertaining the preceding equation, I made some further investigation.It is imperative that, if the assumption is correct, the following equatiOil 51.ould also hold good.Thus one molecule of cysteine must be equivalent to 7 molec~les of sodium hydroxide.To ascertain the relation, two samples of cysteine hydrochloride containing 0.0,88 g. each were prepared. The one was directly titrated with N/"o NaOII, uSIng azolithmine a~ indicator, and the other, after treating with bromine water until a very faintly yellow color was obtained, was also titrated. The results were as follows: bil~e~t tit~~tion ... After treating with the bromineThe difference ...