ABSTRACT
Soluble copper-containing amine oxidases (AOs) from mammals are dimeric proteins that react with a ping-pong mechanism consisting of enzyme reduction by primary amines and subsequent re-oxidation by molecular oxygen:
In addition to a metal, an AO contains an organic prosthetic group, trihydroxyphenylalanine quinone (Janes et al., 1990). Preliminary information about the structural organization of BSAO was obtained from a study of the complex thermal unfolding behavior of the protein by differential scanning calorimetry (Giartosio et al., 1988). The thermodynamic study revealed that the dimer is the fundamental cooperative unit. At least four different domains were recognized. Taking the transition enthalpy change as an indication of domain site, it was possible to dene two sets of domains
similar in pair. The two large domains differ in thermostability by only 1 to 2 degrees, while the melting temperatures of the two smaller domains differ by 20 degrees. Removal of copper displaces at least the two transitions with higher stability and produces a broad peak characterized by a greater increase in heat capacity than normal for globular proteins. The dramatic change in the endotherm after the removal of copper indicates a structural role of the metal cofactor.
