Purification and characterization of a wound-inducible cell wall cationic peroxidase from carrot roots

We have isolated a novel cell wall, cationic peroxidase (pI > 9.3) from roots of the carrot plant, Daucus carota. The purified isozyme, referred to as CP > 9.3, has a molecular mass of 45 kilodaltons and an Reinheitzahl value of 2.3. Amino-acid composition analysis and N-terminal sequencing have been performed with CP > 9.3. The N-terminal sequence shows no homology to any sequence in the protein and nucleic acid data banks. CP > 9.3 activity is induced by wounding in carrot leaves and petioles; this activity is also present in carrot roots but is unaltered by wounding. Enhanced CP > 9.3 activity is seen at 12 hr post-wounding and continues for at least 60 hr in leaves and petioles. Based on studies using cycloheximide, early activation of CP > 9.3 is not due to de novo protein synthesis, but rather to enzyme activation. Temperature and pH optima for CP > 9.3 using guaiacol as a substrate have been determined to be 32 degrees C and 4.9.