Characterization of the Spectroscopic Properties of the Cu,Co Cluster in a Prokaryotic Superoxide Dismutase

A Cu,Co derivative of the Cu,ZnSOD fromPhotobacterium leiognathi,in which cobalt has been selectively substituted for zinc, has been prepared and spectroscopically investigated. The derivative shows three bands in the visible region at 530, 566, and 600 nm when copper is in the oxidized state. Reduction or depletion of the copper ion produce a shift of the band absorbing at 600 to 590 nm because of the detachment from copper of the imidazolate bridging the two metals when copper is in the oxidized state. Numerous isotropically shifted1H NMR lines are observed when copper is oxidized, confirming the presence of the imidazolate bridge between the two metals. Comparison of the optical and the NMR spectra with those observed for the eukaryotic enzyme reveals the occurrence of slight but unambiguous differences diagnostic of a different degree of distortion of the metal cluster between the prokaryotic and eukaryotic enzymes.