The CuA center of cytochrome-c oxidase: electronic structure and spectra of models compared to the properties of CuA domains.

Abstract

The electronic structure and spectrum of several models of the binuclear metal site in soluble CuA domains of cytochrome-c oxidase have been calculated by the use of an extended version of the complete neglect of differential overlap/spectroscopic method. The experimental spectra have two strong transitions of nearly equal intensity around 500 nm and a near-IR transition close to 800 nm. The model that best reproduces these features consists of a dimer of two blue (type 1) copper centers, in which each Cu atom replaces the missing imidazole on the other Cu atom. Thus, both Cu atoms have one cysteine sulfur atom and one imidazole nitrogen atom as ligands, and there are no bridging ligands but a direct Cu-Cu bond. According to the calculations, the two strong bands in the visible region originate from exciton coupling of the dipoles of the two copper monomers, and the near-IR band is a charge-transfer transition between the two Cu atoms. The known amino acid sequence has been used to construct a molecular model of the CuA site by the use of a template and energy minimization. In this model, the two ligand cysteine residues are in one turn of an a-helix, whereas one ligand histidine is in a loop following this helix and the other one is in a a-strand.

In situ characterization of cofacial Co(IV) centers in Co 4 O 4 cubane: Modeling the high-valent active site in oxygen-evolving catalysts

“…Comparing a valence-localized dimer with a valence-delocalized dimer, n is expected to be halved whereas Δr is expected to be doubled (n mon /n dim ∼ 0.5 and Δr mon / Δr dim ∼ 2), so λ i should be roughly twice as large for a localized oxidation process, assuming similar force constants (46)(47)(48). The DFT calculated values of λ i (1b) are in agreement with this prediction, with a reorganization energy for a charge-localized cubane twice that of a charge-delocalized cubane.…”

Soluble CuA Domain of Cyanobacterial Cytochrome c Oxidase

“…At pH 7.0 it exhibits two strong absorbance maxima at 482 nm and 535 nm, respectively. It was suggested that these two absorption bands arise from an interaction between the two Cu ions (60). Two additional maxima are present at 359 nm and 785 nm (Fig.…”

Copper A of Cytochrome c Oxidase, A Novel, Long‐Embattled, Biological Electron‐Transfer Site

“…Thus soluble subunit 11 fragments could be obtained which contained the Cu, site. As the hemes and Cu, are located in the membrane-bound portions, optical and EPR spectra of Cu,, unimpaired by other chromophores, could be obtained [24,[64][65][66]. By recombinant methods it also became possible to build Cu, sites into native proteins or fragments thereof [63, 67, 681.…”

“…However, they also proposed a third bridging ligand, an oxygen species. The third paper [64] was mainly based on the theoretical evaluation by the method of complete neglect of differential overlapkpectroscopic of a model of the Cu, site. The Cu, site can be considered as being built up from two type 1 sites in which each Cu atom replaces a missing His on the other Cu atom.…”