Glutathione reductase was purified from a yeast. Hansenula mrakii IFO 0895, to approximately 3500-fold with 59% activity yield. The enzyme was homogeneous on polyacrylamide gel electrophoresis. The molecular weight of the enzyme was estimated to be 56 kDa by SDS-polyacrylamide gel electrophoresis, and 123 kDa by gel filtration using a calibrated Sephadex G-150 column. The Km values for glutathione disulfide and NADPH were 21.3 microM and 14.3 microM, respectively. The enzyme was most active at pH 7.5, 55 degrees C. The enzyme was stable up to 40 degrees C, and between pHs 4 and 10. The enzyme was inhibited by p-chloromercuribenzoate and metal ions such as Fe3+, Cd2+, Cu2+, and Zn2+.