Far-Red Resonance Raman Study of Copper A in Subunit II of Cytochrome c Oxidase

The present work employs far-red resonance Raman spectroscopy (RR) to investigate whether a Cu-Cu bonding interaction exists in Cu{sub A}. The electronic transition of Cu{sub A} near 830 nm provides the opportunity for specific RR observation of the vibrations of this chromophore. We have employed RR with Cu isotopic substitution on genetically modified, solubilized forms of CcO subunit II from Bacillus subtilis and Paracoccus denitrificans. We have also probed the Cu{sub A} site of native beef heart CcO for comparison. The similarity of the CcO and Cu{sub A} fragment (subunit II) spectra suggests that Cu{sub A} in the isolated subunit II has essentially the same structure as that of Cu{sub A} in intact CcO. Thus, the suggested Cu-Cu bonding in Cu{sub A}, if correct, applies both to the isolated subunit II and native CcO. The functional reasons why nature may choose such a structure, or in fact why a two-copper center of any sort is constructed to perform a function which is commonly believed to be simple one-electron transfer, are unclear. 34 refs., 1 fig., 1 tab.