The D-galactose oxidase of Polyporus circinatus.

The mold Polyporus circinatus produces an extracellular oxidase that catalyzes the oxidation of n-galactose (1). The reaction appears superficially to be similar to the oxidation of n-glucose catalyzed by notatin (2)) and can be followed by measuring the consumption of oxygen or the production of Hz02 (1). The enzyme is useful for the determination of galactose, employing the same peroxidase-chromogen reagent which has been introduced for the assay of glucose with notatin (3). In other respects, however, the reaction is quite different from that catalyzed by notatin. The enzyme does not possess a flavin prosthetic group, and preliminary evidence suggests that it may be a metalloprotein. The most important difference, however, is that oxidation of n-galactose occurs not at the C-l but at the C-6 position, with the formation of n-gal&o-hexodialdose rather than the corresponding hexonic acid (4). Indeed, n-galactose itself may not be the natural substrate for the enzyme, which exhibits a much higher afiity for galactosides and polysaccharides containing galactose end groups.