Cytochromeo3 hemepocket relaxation subsequent to carbon monoxide photolysis from fully reduced and mixed valence cytochromebo3 oxidase

Resonance Raman detection of the Fe2+-C-N modes in heme-copper oxidases: a probe of the active site

Resonance Raman spectroscopy has been employed to investigate the reduced cyano complexes of cytochrome aa(3) from bovine heart and Rhodobacter sphaeroides and of cytochrome bo(3) from E. coli. In the aa(3)-type oxidases, the frequency of the Fe-CN stretching mode is located at 468 cm(-1), and the bending Fe-C-N vibration, at 500 cm(-1). The fully reduced cytochrome bo(3)-CN complex gives rise to a stretching vibration at 468 cm(-1), a bending vibration at 491 cm(-1), and a stretching C-N vibration at 2037 cm(-1). The observed differences between aa(3) and bo(3) oxidases in the frequencies of the Fe-C-N group suggest a quantitative difference in the structure of the His-heme a(3)(2+)/Cu(B)(1+) and His-heme o(3)(2+)/Cu(B)(1+) binuclear pockets upon CN- binding.

Oxygen-linked equilibrium CuB-CO species in cytochrome ba3 oxidase from thermus thermophilus. Implications for an oxygen channel ar the CuB site

We report the first study of O(2) migration in the putative O(2) channel of cytochrome ba(3) and its effect to the properties of the binuclear heme a(3)-Cu(B) center of cytochrome ba(3) from Thermus thermophilus. The Fourier transform infrared spectra of the ba(3)-CO complex demonstrate that in the presence of 60-80 micro m O(2), the nu(C-O) of Cu(B)1+-C-O at 2053 cm(-1) (complex A) shifts to 2045 cm(-1) and remains unchanged in H(2)O/D(2)O exchanges and in the pH 6.5-9.0 range. The frequencies but not the intensities of the C-O stretching modes of heme a(3)-CO (complex B), however, remain unchanged. The change in the nu(C-O) of complex A results in an increase of k(-2), and thus in a higher affinity of Cu(B) for exogenous ligands. The time-resolved step-scan Fourier transform infrared difference spectra indicate that the rate of decay of the transient Cu(B)1+-CO complex at pH 6.5 is 30.4 s(-1) and 28.3 s(-1) in the presence of O(2). Similarly, the rebinding to heme a(3) is slightly affected and occurs with k(2) = 26.3 s(-1) and 24.6 s(-1) in the presence of O(2). These results provide solid evidence that in cytochrome ba(3), the ligand delivery channel is located at the Cu(B) site, which is the ligand entry to the heme a(3) pocket. We suggest that the properties of the O(2) channel are not limited to facilitating ligand diffusion to the active site but are extended in controlling the dynamics and reactivity of the reactions of ba(3) with O(2) and NO.

Observation of the equilibrium CuB-CO complex and functional implications of the transient heme a3 propionates in cytochrome ba3-CO from Thermus thermophilus. Fourier transform infrared (FTIR) and time-resolved step-scan FTIR studies

We report the first evidence for the existence of the equilibrium Cu(B)1+-CO species of CO-bound reduced cytochrome ba(3) from Thermus thermophilus at room temperature. The frequency of the C-O stretching mode of Cu(B)1+-CO is located at 2053 cm(-1) and remains unchanged in H(2)O/D(2)O exchanges and, between pD 5.5 and 9.7, indicating that the chemical environment does not alter the protonation state of the Cu(B) histidine ligands. The data and conclusions reported here are in contrast to the changes in protonation state of Cu(B)-His-290, reported recently (Das, T. K., Tomson, F. K., Gennis, R. B., Gordon, M., and Rousseau, D. L. (2001) Biophys. J. 80, 2039-2045 and Das, T. P., Gomes, C. M., Teixeira, M., and Rousseau, D. L. (1999) Proc. Natl. Acad. Sci. U. S. A. 96, 9591-9596). The time-resolved step-scan FTIR difference spectra indicate that the rate of decay of the transient Cu(B)1+-CO complex is 34.5 s(-1) and rebinding to heme a(3) occurs with k(2) = 28.6 s(-1). The rate of decay of the transient Cu(B)1+-CO complex displays a similar time constant as the absorption changes at 1694(+)/1706(-), attributed to perturbation of the heme a(3) propionates (COOH). The nu(C-O) of the transient Cu(B)1+-CO species is the same as that of the equilibrium Cu(B)1+-CO species and remains unchanged in the pD range 5.5-9.7 indicating that no structural change takes place at Cu(B) between these states. The implications of these results with respect to proton pathways in heme-copper oxidases are discussed.

The role of the cross-link His-Tyr in the functional properties of the binuclear center in cytochrome c oxidase

Resonance Raman and Fourier transform infrared spectroscopies have been used to study the aa(3)-type cytochrome c oxidase and the Y280H mutant from Paracoccus denitrificans. The stability of the binuclear center in the absence of the Tyr(280)-His(276) cross-link is not compromised since heme a(3) retains the same proximal environment, spin, and coordination state as in the wild type enzyme in both the oxidized and reduced states. We observe two C-O modes in the Y280H mutant at 1966 and 1975 cm(-1). The 1975 cm(-1) mode is assigned to a gamma-form and represents a structure of the active site in which Cu(B) exerts a steric effect on the heme a(3)-bound CO. Therefore, the role of the cross-link is to fix Cu(B) in a certain configuration and distance from heme a(3), and not to allow histidine ligands to coordinate to Cu(B) rather than to heme a(3), rendering the enzyme inactive, as proposed recently (Das, T. K., Pecoraro, C., Tomson, F. L., Gennis, R. B., and Rousseau, D. L. (1998) Biochemistry 37, 14471-14476). The results provide solid evidence that in the Y280H mutant the catalytic site retains its active configuration that allows O(2) binding to heme a(3). Oxygenated intermediates are formed by mixing oxygen with the CO-bound mixed-valence wild type and Y280H enzymes with similar Soret maxima at 438 nm.

Kinetics of electron and proton transfer during O(2) reduction in cytochrome aa(3) from A. ambivalens: an enzyme lacking Glu(I-286)

Acidianus ambivalens is a hyperthermoacidophilic archaeon which grows optimally at approximately 80 degrees C and pH 2.5. The terminal oxidase of its respiratory system is a membrane-bound quinol oxidase (cytochrome aa(3)) which belongs to the heme-copper oxidase superfamily. One difference between this quinol oxidase and a majority of the other members of this family is that it lacks the highly-conserved glutamate (Glu(I-286), E. coli ubiquinol oxidase numbering) which has been shown to play a central role in controlling the proton transfer during reaction of reduced oxidases with oxygen. In this study we have investigated the dynamics of the reaction of the reduced A. ambivalens quinol oxidase with O(2). With the purified enzyme, two kinetic phases were observed with rate constants of 1.8&z.ccirf;10(4) s(-1) (at 1 mM O(2), pH 7.8) and 3. 7x10(3) s(-1), respectively. The first phase is attributed to binding of O(2) to heme a(3) and oxidation of both hemes forming the 'peroxy' intermediate. The second phase was associated with proton uptake from solution and it is attributed to formation of the 'oxo-ferryl' state, the final state in the absence of quinol. In the presence of bound caldariella quinol (QH(2)), heme a was re-reduced by QH(2) with a rate of 670 s(-1), followed by transfer of the fourth electron to the binuclear center with a rate of 50 s(-1). Thus, the results indicate that the quinol donates electrons to heme a, followed by intramolecular transfer to the binuclear center. Moreover, the overall electron and proton-transfer kinetics in the A. ambivalens quinol oxidase are the same as those in the E. coli ubiquinol oxidase, which indicates that in the A. ambivalens enzyme a different pathway is used for proton transfer to the binuclear center and/or other protonatable groups in an equivalent pathway are involved. Potential candidates in that pathway are two glutamates at positions (I-80) and (I-83) in the A. ambivalens enzyme (corresponding to Met(I-116) and Val(I-119), respectively, in E. coli cytochrome bo(3)).