Soybean peroxidase as an effective bromination catalysts

Soybean peroxidase (SBP), an acidic peroxidase isolated from the seed coat, has been shown to be an effective catalyst for the oxidation of a variety of organic compounds. In the present study, we demonstrate that SBP can cat alyze halogenation reactions. In the presence of H2O2, SBP catalyzed the ox idation of bromide and iodide but not chloride. Veratryl alcohol (3,4-dimet hoxybenzyl alcohol) served as a useful substrate for SBP-catalyzed halogena tions yielding the 6-bromo derivative. Halogenation of veratryl alcohol was optimal at pHs below 2.5 with rates of 2.4 mu m/min, achieving complete co nversions of 150-mu m veratryl alcohol in 24 h, The enzyme showed essential ly no brominating activity at pHs above 5.5, SBP-catalyzed bromination of v eratryl alcohol proceeded with a maximum reaction velocity, V-max)(apparent ), of 5.8 x 10(-1) mu m/min, a K-m of 78 mu m and a catalytic efficiency (k (cat)/K-m of 1.37 x 10(5) M/min at pH 4.0, assuming all of the enzyme's act ive sites participate in the reaction. SBP also catalyzed the bromination o f several other organic substrates including pyrazole to produce a single p roduct l-bromopyrazole, indole to yield both 5-bromoindole and 5-hydroxyind ole, and the decarboxylative bromination of 3,4 dimethoxy-trans-cinnamic ac id to trans-2-bromo-1-(3,4 dimethoxyphenyl)ethylene A catalytic mechanism f or SBP-catalyzed bromination has been proposed based on experimental result s in this and related studies. (C) 2000 Elsevier Science Inc. All rights re served.