A novel cationic peroxidase (VanPrx) from a hemi-parasitic plant (Viscum angulatum) of Western Ghats (India): Purification, characterization and kinetic properties

Peroxidases are oxido-reductases that have industrial applications. Hemi-parasitic plants which experience continuous oxidative-stress may serve as a source for novel peroxidases. A wild endemic hemi-parasitic plant (Viscum angulatum) from the Western Ghats (India), was selected and the cationic peroxidase VanPrx (p19.6) was isolated and purified. Analyses of trypsin digested peptides by LC-MS/MS confirmed that Van Prx was a Class III peroxidase. Further, the matrix assisted laser desorption ionizationtime of flight (MALDI-TOF) analysis showed its molecular weight as 46.42 kDa. The ultraviolet/visible absorption spectrum is characteristic of heme containing plant peroxidases with a soret peak at 403 nm and R/Z value of 3.1. Different redox states of VanPrx are not similar to those of Class III peroxidases. Unlike HRP, its Compound I was relatively unstable. Further, it did not show formation of Compound III on addition of high concentration of NADH (200 times the molar concentration of enzyme). In contrast to that of classical plant peroxidases, N-terminal sequence of VanPrx was neither conserved nor blocked by pyroglutamate. Kinetic studies with twelve electron donors showed that Van Prx possessed high activity towards substrates of different chemical nature (viz. guaiacol, ferulic acid, ABTS, etc.). Unlike most cationic peroxidases, a significantly high activity of VanPrx with hydroxycinnamic acid derivatives rather than hydroxycinnamyl alcohols indicates its involvement in suberization. Suberization is associated with seed germination and establishment of haustoria of parasitic plants on the host plant. Unlike other cationic peroxidases, lack of IAA oxidase activity in VanPrx may be associated with the absence of root system in V. angulatum. VanPrx is highly thermo stable and retains partial activity even after an 80 degrees C treatment for 10 min. Inhibition kinetics revealed that unlike HRP, VanPrx is not inhibited by EDTA. Furthermore, TEMED a competitive inhibitor of HRP inhibited VanPrx uncompetitively. The present study identifies an endemic hemi-parasitic plant as a source of a novel isoform of Class III peroxidase with distinct substrate affinity, redox states, inhibition kinetics of some of the inhibitors and high thermostability. (C) 2011 Elsevier B.V. All rights reserved.