Abstract
Previously we reported that CWPO-C (cationic cell-wall-peroxidase) from poplar oxidizes sinapyl alcohol and polymeric substrates unlike other plant peroxidases. The characteristics of CWPO-C indicate that the catalytic mechanism is quite different from other peroxidases.
In this study, we investigated the catalytic mechanism of CWPO-C by the homology modeling and chemical modification technique. The chemical modification toward Tyr decreased guaiacol oxidation ability of CWPO-C, whereas it did not affect that of HRP. Interestingly, the Tyr modification for CWPO-C strongly decreased the oxidation of syringaldazine and 2,6-dimethoxyphenol rather than the guaiacol oxidation. Furthermore, TNM-modified CWPO-C did not oxidize ferrocytochrome c. These results indicate that Tyr residue mediates the oxidation of macromolecule substrates. The homology modeling shows that Tyr177 and Tyr74 locate near the heme and are exposed on the protein surface among four Tyr residues in CWPO-C. These results suggest that Tyr177 and/or Tyr74 residue is the active site of CWPO-C.
