The multicopper oxidase from the hyperthermophilic archaeonPyrobacu-lum aerophilum (McoP) was overproduced in Escherichia coliand purified to homogeneity. The enzyme consists of a single kDa subunit, and the combined results of UV–visible, CD, EPR and resonance Raman spectroscopies showed the characteristic features of the multicopper oxidases. Analysis of the McoP sequence allowed its structure to be derived by comparative modeling methods.