Abstract
1 mg% solutions of thiamine mixed with a sufficient amount of buffers between pH 6 and 13,were converted into thiochrome with varied yields by the addition of ferricyanide immediately after mixing. There was found two maximal points for yielding thiochrome, e.g. at pH 9〜10 and over pH 13. Thiamine was left partly unchanged at pH less than 9 and it was chiefly transformed into thiamine disulfide at pH between 11 and 12. If the buffered solution of thiamine was kept standing for 5 minutes at pH 11.5,its oxidation into thiamine disulfide by addition of ferricyanide was nearly complete and no thiochrome was formed, but formation of thiochrome was still observed at its optimal pH at 9 or over 13 even after standing for 30 minutes, although the quicker decrease of thiochrome formation happened over pH 13. As formation of thiamine disulfide was always demonstrated even at the optimal pH for thiochrome-formation, it was concluded that ferricyanide-oxidation of thiamine resulted in thiochrome and thiamine disulfide, to variable proportions, whereas the former was maximal over pH 13 and the latter maximal at pH 11.5.
