Submitted to: Phytochemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/10/2009
Publication Date: 1/1/2010
Publication URL: http://hdl.handle.net/10113/37593
Citation: Violante-Mota, F., Moran, J.F., Sarath, G., Areedondo-Peter, R. 2010. Analysis of the Peroxidase Activity of Rice (Oryza Sativa) Recombinant Hemoglobin 1: Implications for the In Vivo Function of Hexacoordinate Non-Symbiotic Hemoglobins in Plants. Phytochemistry. 71(1):21-26. Interpretive Summary: All plants contain non-symbiotic hemoglobins (nsHbs). There is still considerable debate on their roles within plants. In this study we have shown that nsHbs display poor enzymatic activity against hydrogen peroxide. Our data indicates that ns-Hbs are unlikely to function as peroxidases in planta.
Technical Abstract: In plants, it has been proposed that hexacoordinate (class 1) non-symbiotic Hbs (nsHb-1) function in vivo as peroxidases. However, little is known about the peroxidase activity of nsHb-1. We evaluated the peroxidase activity of rice recombinant Hb1 (a nsHb-1) by using the guaiacol/H2O2 system at pH 6.0. Results showed that the affinity of rice Hb1 for H2O2 was 148-times lower than that reported for HRP (Km = 16.27 and 0.11 mM, respectively) and that the catalytic efficiency of rice Hb1 for the oxidation of guaiacol using H2O2 as electrons donor was 13,443-times lower than that reported for HRP (kcat/Km = 16.23 and 218,181 mM-1 min-1, respectively). Also, results from this work showed that rice Hb1 is not chemically modified and binds CO after incubation with high H2O2 concentration, and that it poorly protects recombinant Escherichia coli from H2O2 stress. These observations indicate that rice Hb1 inefficiently scavenges H2O2 as compared to a typical plant peroxidase, and indicates that non-symbiotic Hbs are unlikely to function as peroxidases in planta.