Screening and partial immunochemical characterization of sulfite oxidase from plant source

Sulfite oxidase [SO; EC 1.8.3.1] catalyses the physiologically vital oxidation of sulfite to sulfate, the terminal reaction in degradation of sulfur containing amino acids, cysteine and methionine. Sulfite oxidase from vertebrate sources is among the best studied molybdenum enzymes. Existence of SO in plants has been established recently by identification of a cDNA from Arabidopsis thaliana encoding a functional SO. The present study was undertaken to identify herbaceous and woody plants (viz., Azardirachta indica L., Cassia fistula L., Saraca indica L., Spinacea oleracea L., and Syzyzium cumini L.), a relatively less explored source, having significant SO activity and to characterize some of its immuno-biochemical properties. The Syzyzium cumini was chosen to characterize SO as it showed maximum enzyme activity in the crude extract as compared to other plants. Absorption spectra of SO revealed two peaks at 235 and 277 nm, but no distinct peak in the visible region could be observed. Crude extract of all the plants were taken into considerations for immuno-biochemical studies. Despite of significant protein structure-functional similarities between plant and animal SO, no cross-reactivity could be established between the two sources of SO. These data suggested that plants SO, however, differed with regards to their immunobiochemical properties.