An EPR study on the conformation of the copper sites of Japanese lacquer-tree laccase

Abstract

At liquid nitrogen temperature, the electron paramagnetic resonance (EPR) spectrum of type 1 Cu, in the type 2 Cu depleted Japanese laccase, was modified in a similar way by addition of urea, azide, or by acidification to pH ⩽ 4.5. The same effect on the type 1 Cu spectrum was produced in the native enzyme by urea or azide. The EPR parameters in the g region became similar to those measured at room temperature, which are different from those measured at liquid nitrogen [L. Morpurgo, E. Agostinelli, M. Senepa, and A. Desideri, J. Inorg. Biochem. 24, 1 (1985)]. It is believed that urea, azide, and low pH prevent the formation, at low temperature, of an additional hydrogen bond between protein residues, responsible for a local conformational change involving the type 1 Cu. The type 2 Cu EPR spectrum was not significantly affected by urea and pH.