title: Time-resolved magnetic circular dichroism spectroscopy of photolyzed carbonmonoxy cytochrome c oxidase (cytochrome aa3).
abstract: Nanosecond time-resolved magnetic circular dichroism (TRMCD) and time-resolved natural circular dichroism (TRCD) measurements of photolysis products of the CO complex of eukaryotic cytochrome c oxidase (CcO-CO) are presented. TRMCD spectra obtained at 100 ns and 10 microseconds after photolysis are diagnostic of pentacoordinate cytochrome a3Fe2+, as would be expected for simple photodissociation. Other time-resolved spectroscopies (UV-visible and resonance Raman), however, show evidence for unusual Fea3(2+) coordination after CO photolysis (Woodruff, W. H., O. Einarsdóttir, R. B. Dyer, K. A. Bagley, G. Palmer, S. J. Atherton, R. A. Goldbeck, T. D. Dawes, and D. S. Kliger. 1991. Proc. Nat. Acad. Sci. U.S.A. 88:2588-2592). Furthermore, time-resolved IR experiments have shown that photodissociated CO binds to CuB+ prior to recombining with Fea3(2+) (Dyer, R. B., O. Einarsdóttir, P. M. Killough, J. J. López-Garriga, and W. H. Woodruff. 1989. J. Am. Chem. Soc. 111:7657-7659). A model of the CcO-CO photolysis cycle which is consistent with all of the spectroscopic results is presented. A novel feature of this model is the coordination of a ligand endogenous to the protein to the Fe axial site vacated by the photolyzed CO and the simultaneous breaking of the Fe-imidazole(histidine) bond.
authors.affiliation: Department of Chemistry and Biochemistry, University of California, Santa Cruz 95064.
authors.forename: R A
authors.initials: RA
authors.lastname: Goldbeck
authors.forename: T D
authors.initials: TD
authors.lastname: Dawes
authors.forename: O
authors.initials: O
authors.lastname: Einarsdóttir
authors.forename: W H
authors.initials: WH
authors.lastname: Woodruff
authors.forename: D S
authors.initials: DS
authors.lastname: Kliger
mesh_terms: D001665:Binding Sites; D001718:Birefringence; D002248:Carbon Monoxide / Q000378:metabolism; D002942:Circular Dichroism; D003576:Electron Transport Complex IV / Q000378:metabolism* / Q000528:radiation effects; D007700:Kinetics; D008280:Magnetics; D010782:Photolysis; D011487:Protein Conformation; D013997:Time Factors
chemical_list: D002248:Carbon Monoxide; D003576:Electron Transport Complex IV