Isolation and characterization of a thermostable intracellular enzyme with peroxidase activity from Bacillus sphaericus

During a screening for bacteria producing enzymes with peroxidase activity, a Bacillus sphaericus strain was isolated. This strain was found to contain an intracellular enzyme with peroxidase activity. The native enzyme had a molecular mass of above 300 kDa and precipitated at a salt concentration higher than 0.1 M. Proteolytic digestion with trypsin reduced the molecular mass of the active enzyme to 13 kDa (dimer) or 26 kDa (tetramer) and increased its solubility, allowing purification to homogeneity. Spectroscopic investigations showed the enzyme to be a hemoenzyme containing heme c as the covalently bound prosthetic group. The enzyme was stable up to 90 °C and at alkaline conditions up to pH 11, with a pH optimum at pH 8.5. It could be visualized by activity staining after SDS-PAGE and showed activity with a number of typical substrates for peroxidases, e.g., 2,2′-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid) diammonium salt, guaiacol and 2,4-dichlorophenol; however the enzyme had no catalase and cytochrome c peroxidase activity.