Spectroscopic studies on the interaction between azide and PPO II from Nicotiana tobacum

N-3(-) is a kind of ligand with very strong power for coordination, and is able to bind with many kinds of metal ions or metalloproteins. The metal ions in metalloproteins usually locate at the active site of them, and the combination of other chemical compound (s) to them will cause great influence on the structure and function of them. In addition, the combination can also provide information of the structure of the active site of the enzymes, and that of the higher-order structure of the enzyme. In this paper, we studied the interaction between N-3(-) and PPO II from Nicotina Tobacco by the determination of changes in enzymatic activity, UV-Vis, fluorescence spectra and FT-IR. The results showed that N-3(-) Can activate PPO U with a near linear increase in enzymatic activity to the concentration of N-3(-) when the [N-3(-)]/[PPO II](molar/molar) is less than or equal to 1.0, and that the enzymatic activity begins to decrease from 1.0 to 4.0; N-3(-),- didn't coordinate directly with Cu2+ in the active site, but may interact with the side chain groups with positive charges, and further resulted in the increase in alpha-helix and the slightly decrease in beta-turn, random coil and extended chain; the Cu2+ may locate deeply in the inner part of PPO II, and coordinates strongly with nitrogen atoms in imidazole of histidine; N-3(-) can quench the fluorescence of PPO II, and make the microenvironments of Trp residues more polar after the interaction between N-3(-) PPO II.