Bovine heart redox-active metal sites

X-ray structures of 2.8-A resolution of bovine heart cytochrome c oxidase with the metals in the fully oxidized state were reported in 1995 (Tsukihara et al., 1995). The X-ray structure of cytochrome c oxidase from Paracoccus denitrificans in the fuUy oxidized azide-bound state at 2.8-A resolution was also published in the same week (Iwata et al., 1995). The structure and location of the metal sites of the two enzymes are astonishingly similar at that resolution. Later, the resolution of the bovine enzyme structure was improved to 2.3A (Yoshikawa et al., 1998). However, resolution of the Paracoccus enzyme has been improved to 2.7-A resolution (Ostermeier et al., 1997). Recently another bacterial ba3-type oxidase at 2.3-A resolution (Soulimane et al., 2000) and Escherichia coli quinol oxidase at 3.5-A resolution were reported (Abramson et al., 2000). X-ray structures of the protein and its redox-active metal sites are discussed in terms of the bovine enzyme below. 

CuA-centers are found in cytochrome c oxidases and in N20-reductase [40,41]. In both enzyme classes, CuA-centers subtract electrons from an external donor and transfer them either directly to the active site or indirectly via a further redox-active center [42-44]. Until recently, knowledge concerning the structure of CuA-centers was incomplete. This situation was alleviated by the publication of the crystal-structures of cytochrome c oxidase from Paracoccus denitrificans and bovine heart in 1995 [43,44]. According to these data, CuA-centers contain [2Cu-2S] structures similar to those in [2Fe-2S]-type iron-sulfur clusters. Both sulfur ligands are donated by cysteine residues in the peptide chain and form a planar structure with the copper ions [43-45]. In both structures, an electron can be delocalized over both metal-ions. In the iron-sulfur center this effect is observed in the reduced form [FeZ5+-Fe2 5+], while in the CuA-center the delo-... 

---