The interaction of azide with polyphenol oxidase II from tobacco.

Spectroscopy studies of absorption and circular dichroism of native PPO II and azide PPO II complex demonstrate two new absorptions at 375 nm and 500 nm after azide's binding with PPO II, which are assigned as the terminal azide to copper charge transfer transitions II(o)nb-to-copper and II(v)nb-to-copper charge transfer transitions respectively. FT-IR spectra also demonstrate that the azide binds in terminal geometry with one of type-3 coppers. The interaction between azide and PPO II is discussed. One terminal azide's binding with one type-3 copper improves the activity of PPO II and the other three azides' further binding in terminal geometry with the type-3 coppers decreases the activity. We theorize that steric hindrance of azides makes oxygen difficult to bind in the active site.