ENZYMATIC OXIDATION OF DIHYDROTHIAMINE:II. OXIDATION BY CRYSTALLINE WHEAT GERM PEROXIDASE

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Using crystalline peroxidase 566 purified from wheat germ, the oxidation of normal-dihydrothiamine to thiamine was investigated and the following results were obtained.1. In the oxidation of dihydrothiamine to thiamine by hydrogen peroxide-peroxidase system, 26 per cent of the dihydrothiamine added was oxidized to thiamine by adding hydrogen peroxide and peroxidase at an adequate time. This reaction was markedly inhibited by hydroxylamine and cyanide.2. The optimal pH of thiamine formation was found to be 4.0, but the maximum was also found at near pH 7.0.3. The amounts of thiamine formed were increased in proportion to the enzyme concentration.4. When pyrocatechol was added to a hydrogen peroxide-peroxidase system, 23 to 24 per cent of dihydrothiamine added was oxidized to thiamine. Peroxidase, hydrogen peroxide and pyrocatechol are all required for this reaction and the amount of vitamin formed was decreased to less than 2 per cent, if any one of these components was omitted. This reaction was also strongly inhibited by hydroxylamine or cyanide.5. Thiamine formation was highest at pH 6 to 7, in accordance with the optimal pH of Peroxidase using guaiacol as a hydrogen donor.6. Thiamine formation was highest, when 0.10 μmole each of hydrogen peroxide and pyrocatechol were added to 0.0016 μmole of peroxidase.7. The amount of thiamine formed was variable when the hydrogen donor was different. It was highest in the case of pyrocatechol and was very low in the case of guaiacol or p-hydroquinone.
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ENZYMATIC OXIDATION OF DIHYDROTHIAMINE:II. OXIDATION BY CRYSTALLINE WHEAT GERM PEROXIDASE

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