Purification and characterization of a peroxidase present in xilopodium exsudates of umbu plants (Spondias tuberosa A.)

Abstract

Umbu plants are drought resistant trees which are able to store water and several other substances into its adapted root, named xylopodium. The exsudate from xilopodium is a natural solution rich in salts, sugars and a little concentration of proteins. In this work, we report the purification of a peroxidase (POX) from umbu xilopodium exsudate by direct extraction from polyacrylamide electrophoresis gels. Umbu POX showed optimum activity at pHs around 6.0 to 7.0 and high thermal resistance after incubation at 70°C for 6 min. POX activity present in crude extracts was more heat-resistant than in its purified form. When assayed with metal ions, umbu POX activity was shown to be inhibited by Mn²⁺ and stimulated by Ca²⁺ and Mg²⁺; it was also inhibited by sodium azide (concentrations higher then 1 mM) and not inhibited by either EDTA or tropolone. POX Km values for guaiacol and methylcatechol substrates were 6.83 and 22.25, respectively. The enzyme is proposed to be a guaiacol peroxidase and was seen to be located at higher concentrations in the outermost layers of xylopodium tissue, such as the endoderm.

Key words: Root enzyme, tissue brownig, guaiacol peroxidase, oxidative metabolism.