Dimerization of ferulic and caffeic acids by purified peroxidase isolated from Bupleurum salicifolium callus culture

A novel peroxidase that catalyses the transformation of caffeic acid and ferulic acid via oxidative coupling was purified from callus cultures of Bupleurum salicifolium petioles. The enzyme, which was purified over 2,900-fold, is a glycoprotein with a molecular weight of 38,000, determined by SDS/PAGE and gel filtration. The K-m values obtained were 2.4 x 10(-4) M for caffeic and 2.6 x 10(-4) M for ferulic acid, while the Km values for H2O2 with caffeic acid was 4 x 10(-5) M and for H2O2 with ferulic acid was 4.8 x 10(-4) M. The purified peroxidase exhibits lower activity with typical peroxidase substrates (guaiacol and pyrogallol) than it does with caffeic and ferulic acids, but does not exhibit any activity with other phenylpropanoids tested (cinnamic acid, coumaric acid, and 3,4-dimethoxycinnamic acid).