Spectroelectrochemical studies of structural changes during reduction of oxygen catalyzed by laccase adsorbed on modified carbon nanotubes

Reduction of oxygen catalyzed by laccase was studied by surface-enhanced infrared absorption spectroscopy (SEIRAS) combined with electrochemical techniques. Laccase molecules were adsorbed on modified carbon nanotubes (CNTs). SEIRAS provided spectra of Amide I band of adsorbed laccase. Fourier self-deconvolution (FSD) and two-dimensional correlation spectroscopy (2D COS) techniques were employed to reveal the sub-band structure of the Amide I band. The analysis demonstrated that laccase adsorbed on CNTs remains its native state both in the oxidized and reduced states. The detailed analysis showed that change of the oxidation state leads to a small change of the secondary structure of the protein. This change is comparable to the change observed for similar blue-copper oxidases in solution during redox titration. The results of this study demonstrated that CNT's immobilized laccase is an excellent catalyst of oxygen reduction. This study illustrates power of quantitative analysis of IR data to provide information about three-dimensional structure of surface immobilized proteins.