Abstract
The pH optimum and kinetic properties of glutathione reductase from rice embryos have been determined. The enzyme was strongly inhibited by sulfhydryl reagents especially when the enzyme was kept contact with the hydrogen donor prior to the addition of in-hibitor. The physical and chemical properties of the enzyme have been characterized. Its sedimentation coefficient, s020, w, and diffusion coefficient, D20, w, were 6.20 S and 5.4 F, respectively. From these values, the molecular weight of the enzyme was calculated to be 106000. On the sodium dodecyl sulfate-polyacrylamide gel electrophoresis the molecular size of the subunit was estimated to be 52000. The flavin prosthetic group of the enzyme was identified as flavin adenine dinucleotide. The flavin content indicated the presence of 1 mole of FAD per 52400 of minimum molecular weight. These results suggest that the enzyme molecule consists of two subunits, each containing 1 mole FAD. The amino acid composition was somewhat similar to that of the yeast enzyme and the content of half cystine residues was the same between the two proteins although the rice glutathione reductase contained the greater amount of hydroxylamino acids than the yeast enzyme. Hydroxyproline was found in the rice enzyme.
