title: Nitrosyl cytochrome c oxidase. Formation and properties of mixed valence enzyme.
abstract: We report the first resonance Raman scattering studies of NO-bound cytochrome c oxidase. Resonance Raman scattering and optical absorption spectra have been obtained on the fully reduced enzyme (a2+, a2+(3) NO) and the mixed valence enzyme (a3+, a2+(3) NO). Clear vibrational frequency shifts are detected in the lines associated with cytochrome a in comparing the two redox states. With 441.6 nm excitation the fully reduced preparation yields a spectrum similar to that of carbon monoxide-bound cytochrome c oxidase and is dominated by the spectrum of reduced cytochrome a. In contrast, in the mixed valence preparation no contributions from reduced cytochrome a are evident in the spectrum, verifying that this heme is no longer in the Fe2+ state. In the mixed valence NO-bound samples, a line appears at approximately 545 cm-1, a frequency similar to that found in NO-bound hemoglobin and myoglobin and assigned as an Fe-N-O-bending mode in those proteins. We do not detect this line in the spectrum of the fully reduced NO-bound enzyme. The carbonyl line of the cytochrome a3 heme formyl group in the fully reduced NO-bound enzyme appears at approximately equal to 1666 cm-1 in the resonance Raman spectrum. In the mixed valence NO-bound preparation the frequency of the carbonyl line increases by 1.2 cm-1 to approximately equal to 1667 cm-1. Thus, modes in cytochrome a2+(3) NO are sensitive to the redox state of the cytochrome a and/or CuA centers. We propose that the redox sensitivity of the formyl mode and the Fe-N-O mode results from an interaction between cytochrome a2+(3) (NO) and the cytochrome a-CuA pair, and is linked to the cytochrome a3 (NO) by the coupling between CuB and the NO-bound cytochrome a3 heme.
authors.affiliation: AT&T Bell Laboratories, Murray Hill, New Jersey 07974.
authors.forename: D L
authors.initials: DL
authors.lastname: Rousseau
authors.forename: S
authors.initials: S
authors.lastname: Singh
authors.forename: Y C
authors.initials: YC
authors.lastname: Ching
authors.forename: M
authors.initials: M
authors.lastname: Sassaroli
mesh_terms: D000818:Animals; D002248:Carbon Monoxide / Q000378:metabolism; D002417:Cattle; D017936:Cytochrome a Group; D003580:Cytochromes; D003576:Electron Transport Complex IV / Q000378:metabolism*; D009569:Nitric Oxide / Q000378:metabolism*; D010084:Oxidation-Reduction; D013059:Spectrum Analysis, Raman
chemical_list: D017936:Cytochrome a Group; D003580:Cytochromes; D009569:Nitric Oxide; D002248:Carbon Monoxide; D003576:Electron Transport Complex IV