Bioelectrocatalyst for O2 Reduction Based on a Novel Recombinant Two-Domain Laccase from Streptomyces ochraceisleroticus Immobilized on Naphthyl-Modified MWCNTs

A novel two-domain small laccasefrom Streptomyces ochraceiscleroticus (SoSL) was produced through recombination in Escherichia coli and purified by affinity chromatography. The properties (thermal optimum and thermostability, pH optima and pH-stability), kinetic characteristics, substrate specificity and dye decolorization ability were estimated. Laccase SoSL was able to oxidize 2,2′-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid (ABTS)and 2,6-dimethoxyphenol (2,6-DMP) with at a maximal rate at pH 3.5 and 9.0, respectively, and was stable at pH 9.0 (retained 75% activity after incubation at room temperature for 120 h). High enzyme affinity to ABTS is caused by an expanded area occupied by aromatic amino acid residues on its surface. Substrate-directed immobilization of the enzyme was performed using naphthylated multiwalled carbon nanotubes (MWCNTs), and a high oxygen reduction reaction potential (+0.62 V vs. normal hydrogen electrode (NHE)) was observed. The above-mentioned features make this enzyme a promising one for further studies in bioremediation and biological fuel cell technologies.