text: The multicopper active site of CP contains a type I (T1) mononuclear copper site and a trinuclear copper center ~ 12-13 Å away (see figure 2).  The tricopper center consists of two type III (T3) coppers and one type II (T2) copper ion.  The two T3 copper ions are bridged by a hydroxide ligand while another hydroxide ligand links the T2 copper ion to the protein.  The T1 center is bridged to the tricopper center by two histidine (His1020, His1022) residues and one Cys(1021) residue.  The substrate binds near the T1 center and is oxidized by the T1 Cu ion forming the reduced Cu oxidation state.  The reduced T1 Cu then transfers the electron through the one Cys and two His bridging residues to the tricopper center.  After four electrons have been transferred from the substrates to the copper centers, an O binds at the tricopper center and undergoes a four-electron reduction to form two molecules of water.