Single crystal absorption spectra of ascorbate oxidase from green zucchini squash

Single crystal polarized absorption spectra of the dimeric multicopper enzyme ascorbate oxidase from green zucchini squash indicate that its most relevant functional and structural properties are maintained in the crystalline state. Since the polarized absorption spectra of crystalline ascorbate oxidase are very similar, in the visible region, to those of crystalline plastocyanin, we expect that structural data will show similar orientation of the type 1 Cu 2+ center with respect to the crystal axes. The selective removal of type 2 Cu 2+ from the crystal has been realized and has a potential value for the identification of the copper centers in the crystallographic analysis of the enzyme. Evidence is presented for an azide binding site formed by type 2 and type 3 Cu 3+, similar to the trinuclear copper center suggested to be present in laccase.