A thermostable humic acid peroxidase from Streptomyces sp. strain AH4: Purification and biochemical characterization

An extracellular thermostable humic acid peroxidase (HaP3) was isolated from a Streptomyces sp. strain AH4. MALDI-TOF MS analysis showed that the purified enzyme was a monomer with a molecular mass of 60,215.18 Da. The 26 N-terminal residues of HaP3 displayed high homology with Streptomyces peroxidases. Optimal peroxidase activity was obtained at pH 5 and 80 °C. HaP3 was stable at pH and temperature ranges of 4–8 and 60–90 °C for 72 and 4 h, respectively. HaP3 catalyzed the oxidation of 2,4-dichlorophenol, commercial humic acid, guiacol, and 2,6-dichlorophenol (50 mM); l-3,4-dihydroxyphenylalanine (40 mM); 4-chlorophenol, 2,4,5-trichlorophenol, and 2,4,6-trichlorophenol (30 mM) in the presence of hydrogen peroxide. Sodium azide and potassium cyanide inhibited HaP3, which indicated the presence of heme components. These properties make HaP3 a potential strong candidate for future application in the elimination of natural humic acids in drinking water.