Identification and molecular characterization of novel peroxidase with structural protein-like properties

Elicitor treatment or mechanical damage to Scutellaria baicalensis Georgi ( skullcap plants) callus causes an immediate insolubilization of a 36-kDa pr otein into cell walls. The 36-kDa protein was identified as peroxidase 1 by analysis of its internal amino acid sequence and by immunoblotting using a ffinity-purified anti-peroxidase 1. Insolubilized peroxidase 1 is cross-lin ked to lignin through covalent bonds, and the cross-linking is catalyzed in the presence of H2O2 by peroxidase 1 itself. The properties of insolubiliz ed peroxidase 1 resemble those of defense-related structural proteins (exte nsins and proline-rich proteins) cross-linked to cell wall. Although the is ozymes peroxidases 2 and 3 have enzyme activities similar to peroxidase 1, they are not insolubilized by stress treatment. Molecular characterization established that peroxidase 1 contains regions characteristic of structural proteins, but peroxidases 2 and 3 do not have such regions. These results suggest that among the three isozymes, only peroxidase 1 has a structural p rotein-like function as well as an enzymatic function.