THE ACTION OF BACTERIAL THIAMINASE I ON THIAMINE

Abstract

Pyrimidinyl-cysteine was detected by paper chromatography when thiamine was decomposed in the presence of cysteine by partially purified thiaminase I prepared from Bacillus thiaminolyticus.The reaction product from thiamine and cysteine by purified thiaminase I was isolated from the reaction mixture in crystalline form, mp 219-220° (decomp.), by means of column chromatography using Amberlite IRC-50. The crystalline substance was found hardly soluble in organic solvents and cold water, but soluble in hot water, and in an acid or alkaline solution. The substance gave positive reaction with both Dragendorff and ninhydrin reagents, but negative with nitroprusside even after treatment with zinc powder in acid solution. Its RF value was shown to be 0.36 by ascending paper chromatography with a n-butanol-methanol-water system (25°, 16hr) when an acid solution of the crystal was spotted.The isolated compound was found to be identical with an authentic sample of pyrimidinyl-cysteine in melting point, elementary analyses, and absorption spectra, etc. The chemical constitution of pyrimidinyl-cysteine was shown to be S-(2-methyl-4-amino-pyrimidinyl-(5)-methyl)-cysteine. S-(2-methyl-4-amino-pyrimidinyl-(5)-methyl)-cysteine sulfoxide, formula II, was obtained as an oxidation product of pyrimidinyl-cystine. The infrared absorption spectrum of the sulfoxide showed the existence of a sulfoxide group in the molecule.It was clearly shown that thiaminase I catalysed an exchange reaction between the thiazole moiety of thiamine and cysteine, probably also other sulfhydryl compounds, besides the well-known base exchange reaction.