Room temperature ESR spectra of Rhus vernicifera laccase and derivatives.

Although both the type 1 and type 2 coppers of Rhus vernicifera laccase are fully ESR detectable at 77 K, only 30% of the type 2 copper are in the cupric form at room temperature. The residual 70% of the type 2 copper was easily transformed into the ESR detectable form by irradiating the resting enzyme with microwave of 200 mW. The enzyme activity did not change by the irradiation with high-powered microwave, indicating that the type 2 copper can be in both the ESR detectable and ESR undetectable forms in solution. The room temperature ESR spectra of the type 2 copper-depleted laccase and of the azide-bound type 3 copper signals were also measured at room temperature and compared with those at 77 K.