Multiple molecular forms of diarylpropane oxygenase, an H2O2-requiring, lignin-degrading enzyme from Phanerochaete chrysosporium

Abstract

Three different molecular forms of the H2O2-requiring heme enzyme, diarylpropane oxygenase, were isolated from the extracellular medium of Na-acetate buffered, agitated cultures of Phanerochaete chrysosporium. Forms I, II, and III were separated by DEAE-Sepharose and further purified on Sephadex G-100. Absorption maxima of the native, reduced, and a variety of ligand complexes of the three enzyme forms are essentially identical, indicating similar heme environments. All forms also have similar, but not identical, reactivity. The homogeneous proteins oxidized a diarylpropane, an olefin, a beta-aryl ether dimer, a phenylpropane, phenylpropane diols, and veratryl alcohol. Identical products were produced from each form. However, the specific activities of the three homogeneous enzymes for veratryl alcohol oxidation were 18.75, 11.80, and 8.48 mumol min-1 mg-1. In the presence of one equivalent of H2O2 the Soret maximum of diarylpropane oxygenase II shifted from 408 to 418 nm, and two additional maxima appeared at 526 and 553 nm, indicating the presence of an Fe(IV)-oxo species equivalent to horseradish peroxidase II. This oxidized species could be reduced back to the native form by veratryl alcohol and several reducing agents (e.g., Na2S2O4, NH2NH2, thiourea, or NADH). The molecular weights of diarylpropane oxygenases I, II, and III were approximately 39,000, 41,000, and 43,000, respectively. The major form (II) (85% of the activity) contained approximately 6% neutral carbohydrate. The affinity of the forms for concanavalin A-agarose suggests that they all are glycoenzymes.