抄録
From the extract of bakers' yeast, menadione reductase was separated, purified and crystallized. This enzyme has fluorescence and has FAD as the prosthetic group. FAD content in this enzyme was 1.12 per cent, giving molecular weight of 70, 000 when one assumes the ratio of one FAD to one enzyme. It has absorption spectrum with maxima at 272, 370, 454 and 457 mμ (shoulder). NADH2 seems to be the specific hydrogen donor to this enzyme while a variety of compounds such as quinones (menadione, p-benzopuinone and ubiquinone Q0), dyes (methylene blue and 2, 6-dichlorophenol-indophenol) and potassium ferricyanide serve as hydrogen acceptors. Optimal pH for the enzyme activity is 5.8-5.9. However, when the enzyme activity is assayed using cytochrome c as in the standard assay system, the optimal pH is 6.5. Antimycin A3 and amytal had no inhibitory effect and dicumarol and NAD lowered the enzyme activity. PCMB reversed the NAD inhibition in the assay system.
The authors wish to thank Dr. M., Matsui, the director of Takamine Laboratory, for his encourage-ment of the work during the course of this investigation and Dr. M., Nakamura, the superintendent of Sankyo Tanashi Plant, for the supply of large quantity of the enzyme source.
