Environmental stress-induced extracellular isoperoxidase RC3 from rice

Effects of various environmental stresses such as heavy metals, salts and low (high) temperature on the secretion of peroxidase isozyme into the medium were examined in rice (Oryza sativa cv. Nak-Dong) suspension culture. The major extracellular peroxidases secreted into the medium by various stresses were cationic isoperoxidases. A far migrating cationic isoperoxidase RC3 was isolated from the medium after application of CaCl2, the effective stimulator for peroxidase secretion. Isolation of extracellular isoperoxidase RC3 was accomplished by ammonium sulfate fractionation, CM-cellulose cation-exchange chromatography, and Sephacryl S-100 gel filtration. The enzyme was a glycoprotein having molecular weight of approximately 34 KDa as determined by SDS-PAGE and 38 KDa by Sephacryl S-100 gel filtration. The pI value of the enzyme was 8.9. Kinetic studies revealed that the optimum pH of the enzyme was 6.0 for guaiacol and H2O2, and the Km values for guaiacol and H2O2 were 10.5 mM and 3.2 mM, respectively.