Structure of valence band in cluster model for cytochrome-c-oxidase active centers

Abstract

The electron structure of cluster model for active centers of cytochrome-c-oxidase has been calculated by DFT (PBE) method in 6-31G basis. The cluster model was constructed on the basis of experimental PDB-structure and included 1105 hemoprotein atoms. The valence band ceiling of cytochromeoxidase active centers is shown to be formed by the atoms of carbon and nitrogen from porphyrin ring of cytochrome heme a ₃ and atoms of carbon and nitrogen from imidazol moieties of histidine connected with Cu atom in cytochrome a ₃. D-orbitals of Cu and Fe atoms from heme a ₃ and d-orbital of Fe atom from heme a contribute mainly to the orbital group. A conclusion is made that the catalytic activity of the structure is determined by these two types of orbitals. Cu d-orbitals of cytochrome a are substantially low in energy. It is suggested that Cu atoms of cytochrome a shift the chemical potential of d-orbitals belonging to the active center that results in their easier electron accepting and releasing. This can be a decisive factor in the electron transport process.