Purification and substrate specificity of peroxidase from sweet potato tubers

Previously the screening of tropical plants demonstrated a high peroxidase activity in sweet potato (Ipomoea batatas) tubers. The major peroxidase pool is localized in peel. Using peel of sweet potato as a source, the sweet potato peroxidase (SPP) has been isolated and purified to homogeneity. The enzyme purification included homogenization, extraction of colored compounds and consecutive chromatographies on Phenyl-Sepharose and DEAE-Toyopearl. The purified SPP had specific activity of 4900 U mg(-1) protein, RZ (ratio of absorbances at 403 and 280 nm, respectively) 3.4, molecular mass of 37 kDa and isoelectric point of 3.5. The spectrum of peroxidase from sweet potato is typical for plant peroxidases with a Soret maximum at 401 nm and the maxima in the visible region at 497 and 638 nm, respectively. The substrate specificity of SPP is distinct from the specificity of other plant peroxidases, ferulic acid being the best substrate for SPP. (C) 2002 Elsevier Science Ireland Ltd. All rights reserved.