Electron paramagnetic resonance of Cu2+:Mb single crystal. Conformational changes.

Copper introduced into met-myoglobin crystals occupies various sites as indicated by electron paramagnetic resonance parameters. Cu2+ (A) is probably liganded to histidine A10, lysine A14, and asparagine GH4 (Banaszak et al., 1965) and shows superhyperfine interaction with a single (imidazole) nitrogen. Cu2+ (B) and Cu2+ (C) correspond to other anisotropic sites described in less detail. Cu2+ (A) exhibits a transition to an isotropic form with a transition temperature of 40.5 degrees C. This transition indicates a conformational change in myoglobin and could correspond to a motion of A helix away from the GH section. The transition temperature is 7 degrees C higher than the one previously reported (Atanasov, 1971) for myoglobin in solution.