Studies on the enzyme glucose oxidase from Penicillium amagasakiense

A short method of purification of P.amagasakiense glucose oxidase has been achieved. Attempts to prepare the apoenzyme were unsuccessful. Inhibition of activity of the holoenzyme by heavy metals was investigated. It was shown that inhibition was due to the metal cations rather than the undissociated metal salts. The effect of bisulphite on the enzyme was shown to be the same as for Aspergillus niger glucose oxidase. From the kinetic experiments with bisulphite, an ionizable group with a pK of 4.2 was found to be involved in the reaction. This pK was assigned to the amino group of adenine of the FAD moiety of the enzyme. Experiments on the binding of halide anions to the enzyme indicated the involvement of an ionizable group with the same pK. Photo-chemical experiments on the enzyme revealed three different phenomena. (1) Photo-oxidation with methylene blue or Rose Bengal as sensitizer, destroyed an ionizable group with pK of 7.2. This was assigned to a histidine residue in the protein. (2) At high pH in the presence of EDTA and with no oxygen present photo-reduction of the enzyme spectrum was obtained. The spectrum of the oxidised enzyme was obtained when air was admitted to the reduced species. (3) At high pH in the presence of EDTA, light at 450 nm wavelength caused the enzyme to lose activity. This activity loss was irreversible with respect to oxygen or glucose. The presence of glucose in the reaction mixture during illumination protected the enzyme from this photo-destruction