Purification and Properties of a New Enzyme,Glutathione Oxidase from Penicillium sp. K-6-5

A new flavoprotein enzyme, GSH oxidase, was found in the aqueous extract of a wheat bran culture of Penicillium sp. K-6-5. The oxidase is also produced extra and intracellularly in the liquid culture, although the production is much lower than that in the wheat bran culture.

The enzyme has been purified to homogeneity. It shows absorption maxima at 270, 350 and 444 nm and a shoulder around 465 nm and contains 2 mol of FAD per mol of enzyme. The enzyme has a molecular weight of approximately 95,000 and consists of two subunits identical in molecular weight (about 47,000). Balance studies show that 2 mol of GSH are converted to 1 mol of GSSG and hydrogen peroxide with the consumption of 1 mol of oxygen. In addition to GSH, several sulfhydryl compounds are oxidized by the enzyme to a lesser extent. The Michaelis constants are as follows: 0.69 mm for GSH, 3.6 mm for l-cysteine and 6.7 mm for dithiothreitol at pH 7.4. The oxidase scarcely acts on reduced RNase A in contrast to the known sulfhydryl oxidases. The isoelectric point and the optimal pH are 4.2 and 7.4, respectively. The enzyme activity is completely inhibited by addition of 1 mm ZnSO₄.