A comparative study of two isoforms of laccase secreted by the "white-rot" fungus Rigidoporus lignosus, exhibiting significant structural and functional differences

Two isoforms of laccase were obtained as the predominant phenol-oxidases in de®ned medium liquid cultures of the ``white-rot'' fungus Rigidoporus lignosus (R. lignosus). A characterization of the two laccases was made in terms of molecular mass, isoelectric point, metal content and N-terminal sequence. Furthermore, in order to gain information on the structural features related to the metal centers, a study of their geometric arrangement and their redox ability was made. It turned out that the two isoenzymes greatly di€ered with regard to pH stability, catalytic and copper centers features. It is proposed that all such di€erences are dependent on the amino acid sequences, which cause a distortion of the copper sites, thus accounting for the redox potential values and kinetic properties.