Femtosecond resolution of ligand-heme interactions in the high-affinity quinol oxidase bd: A di-heme active site?

AUTOR(ES)

Vos, Marten H.

FONTE

The National Academy of Sciences

RESUMO

Interaction of the two high-spin hemes in the oxygen reduction site of the bd-type quinol oxidase from Escherichia coli has been studied by femtosecond multicolor transient absorption spectroscopy. The previously unidentified Soret band of ferrous heme b595 was determined to be centered around 440 nm by selective excitation of the fully reduced unliganded or CO-bound cytochrome bd in the α-band of heme b595. The redox state of the b-type hemes strongly affects both the line shape and the kinetics of the absorption changes induced by photodissociation of CO from heme d. In the reduced enzyme, CO photodissociation from heme d perturbs the spectrum of ferrous cytochrome b595 within a few ps, pointing to a direct interaction between hemes b595 and d. Whereas in the reduced enzyme no heme d-CO geminate recombination is observed, in the mixed-valence CO-liganded complex with heme b595 initially oxidized, a significant part of photodissociated CO does not leave the protein and recombines with heme d within a few hundred ps. This caging effect may indicate that ferrous heme b595 provides a transient binding site for carbon monoxide within one of the routes by which the dissociated ligand leaves the protein. Taken together, the data indicate physical proximity of the hemes d and b595 and corroborate the possibility of a functional cooperation between the two hemes in the dioxygen-reducing center of cytochrome bd.

Documentos Relacionados

• Time-resolved electrometric and optical studies on cytochrome bd suggest a mechanism of electron-proton coupling in the di-heme active site
• Mitochondrial cytochrome c1 is a collapsed di-heme cytochrome
• Ligand specificity of a high-affinity binding site for lipo-chitooligosaccharidic Nod factors in Medicago cell suspension cultures
• High-affinity self-reactive human antibodies by design and selection: targeting the integrin ligand binding site.
• Only high-affinity receptors for interleukin 2 mediate internalization of ligand.