Resonance Raman excitation profiles indicate multiple Cys .fwdarw. Cu charge transfer transitions in type 1 copper proteins

Nitrite reductase (NiR) from Achromobacrer cycloclastes and mutant yeast Cu-Zn superoxide dismutase (with Cys substituted for His80 and Cu for Zn) have both been shown to contain type 1 Cu sites. However, they differ from other type 1 (blue) Cu proteins in that they are green: the absorption band at ∼460 nm is more intense than the one at ∼600 nm. Excitation within either of these absorption bands leads to resonance Raman (RR) spectra that are characteristic of type 1 Cu with a large number of peaks between 250 and 500 cm -1 . The RR spectra of NiR and mutant SOD are thus indicative of a Cu-cysteinate chromophore with a short Cu-S bond distance (∼2.1 A) and a coplanar cysteine moiety (Cu-S γ -C β -C α dihedral angle ∼180 o )