Purification and characterization of sulochrin oxidase from Penicillium frequentans

Sulochrin oxidase, an enzyme catalyzing regio- and stereospecific phenol oxidative coupling reaction to form (+)-bisdechlorogeodin from sulochrin, was isolated from Penicillium frequentans CMI 96659. By chromatographies on DEAE-cellulose, hydroxyapatite, Phenyl-Sepharose, Mono P, Mono Q, and HPLC gel filtration columns, sulochrin oxidase was purified to apparent homogeneity. The purified enzyme had a molecular weight of 230 K as estimated by gel filtration and 110 K as estimated by sodium dodecylsulfate-polyacrylamide gel electrophoresis under denaturing conditions, suggesting that the active enzyme was a homodimer. The enzyme showed pI 4.0 and an optimum pH of 6. The enzyme activity was strongly inhibited by the copper-chelating reagent, diethyldithiocarbamate, and did not recover its full activity even after removing the inhibitor by dialysis. However, enzyme activity was fully restored by the addition of Cu2+. Thus, sulochrin oxidase is considered to be a copper protein. The enzyme showed high substrate specificity for benzophenone compounds such as sulochrin and dihydrogeodin.