Dibenzothiophene (DBT) degrading enzyme responsible for the first step of DBT desulfurization by Rhodococcus erythropolis D-1: Purification and characterization

Rhodococcus erythropolis D-1 possesses an enzymatic pathway that can remove covalently bound sulfur from dibenzothiophene (DBT) to form 2-hydroxybiphenyl. Enzymes involved in DBT degradation, catalyzing the first step of DBT desulfurization, have been identified and purified and characterized. This enzymes convert DBT to DBT sulfone. Enzyme activity was detected when two DEAE-Sepharose column chromatography fractions were combined. One enzyme, designated as component B, was purified from R. erythropolis D-1. Component B was found to have a molecular mass of 250 kDa and consist of six subunits each with a mass of 45 kDa. Analysis of the 20-residue N-terminal amino acid sequence revealed that component B is the dszC product. Other enzyme(s), contained in fraction A, were found to exhibit NADH-linked reductase activity with artificial electron accepters, dichlorophenolindophenol, cytochrome c and ferricyanide. The DBT degrading enzyme exhibits the narrow substrate specificity; it acts on some DBT derivatives but not on DBT analogues, carbazole and fluorene. The DBT degrading enzyme activity is inhibited by 1,10-phenanthroline, 2,2'-bipyridyl, p-chloromercuribenzoic acid, 5,5'-dithiobis(2-nitrobenzoic acid), 8-quinolinol, Mn2+, Cu2+, and Zn2+, suggesting that thiol group(s) and metal(s) might be essential for the enzyme activity. The optimal temperature and pH of this enzyme are 40 degrees C, and about 8.0, respectively.