Cloning and Characterization of Catalases from Rice, Oryza sativa L.

Catalase is the major H2O2-scavenging enzyme in all aerobic organisms. From the cDNA sequences of three rice (Oryza sativa L.) genes that encode for predicted catalases (OsCatA, OsCatB, and OsCatC), complete ORFs were subcloned into pET21a and expressed as (His)(6)-tagged proteins in Escherichia coli. The recombinant (His)(6)-polypeptides were enriched to apparent homogeneity and characterized. With H2O2 as substrate, the highest catalase kat value (20 +/- 1.71 x 10(-3) min(-1)) was found in recombinant OsCatB. The optimum temperatures for catalase activity were 30 degrees C for OsCatA and OsCatC and 25 degrees C for OsCatB, while the pH optima were 8.0, 7.5, and 7.0 for OsCatA, OsCatB, and OsCatC respectively. All the catalases were inhibited by sodium azide, beta-mercaptoethanol, and potassium cyanide, but only weakly by 3-amino-1,2,4-triazole. The various catalases exhibited different catalase activities in the presence of different salts at different concentrations, OsCatC showing higher salt inhibitory effects than the two other OsCats.