observation of Cu-N3- Stretching and N3-Asymmetric Stretching Bands for mono-Azide Adduct of Rhus vernicifera Laccase

Mono-azide adduct of Rhus vermicifera laccase, a multicopper oxidase containing one type-1 (blue) copper, one type-2 (non-blue normal) copper, and a pair of type-3 (binuclear and EPR silent) coppers, of which type-2 and type-3 copers constitute a trinuclear site, was investigated with resonance Raman (RR) and Fourier transform infrared (FT-IR)spectroscopies as a step toward elucidation of the structure and function of the trinuclear site. The Cu-N3- stretching (vCu-N3-) RR band was observed for azide-bound multicopper oxidases for the first time. The vCu-N3- band was located at 400 cm-1 for mono-14N3- laccase, which shifted to 396 cm-1 with the 15N14N14N3- analog. The N3- asymmetric stretching (V(N3-)asym) band was observed by FT-IR spectroscoy at 2035 cm-1 for mono-14N3- laccase and at 2025cm-1 for the 15N14N14N3- analog. The VCu-N3- and V(N3-)asym frequencies and their 15N14N14N- isotypw shifts for azido laccase correspond well with those of metazido hemocyanin, indicating that both derivatives should have a similar binding geometry of azide.