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

Vos, Marten H.; Borisov, Vitaliy B.; Liebl, Ursula; Martin, Jean−Louis; Konstantinov, Alexander A.

doi:10.1073/pnas.030528197

Cited by 61 publications

(93 citation statements)

References 44 publications

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“…First there is a large blue shift of the ferrous heme d ␥-band that gives rise to a maximum at ϳ400 nm (formation of CO-ligated heme d) and a broad minimum centered around 432 nm (decrease in free heme d) with an inflection point around 420 nm between them. This major effect overlaps with a sharp first derivativeshaped feature with a maximum at 436 nm and a minimum at 444 nm dominated by perturbation of the ferrous heme b 595 band at ϳ440 nm induced indirectly by CO binding to heme d (23). As discussed in Ref.…”

Section: Room Temperature Static Spectra-mentioning

confidence: 94%

“…On the other hand, low temperature photodissociation studies carried out by Poole and co-workers (24 -26) on cytochrome bd from different bacteria have revealed consistently a simple pattern of photoinduced spectral changes assigned to the photodissociation of the cytochrome b 595 -CO complex. Recent femtosecond photobleaching studies have identified the Soret band of ferrous heme b 595 at about 440 nm and support this interpretation (23). CO binding with about 15% of heme b 595 at cryogenic temperatures was observed with the aid of Fourier transform infrared spectroscopy in the membrane-bound cytochrome bd from E. coli, but there was no binding in the isolated enzyme (18).…”

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confidence: 89%

“…A difference spectrum of this phase is shown in Fig. 4 by spectrum a, which is typical of CO binding with heme d (including a spectral perturbation of ferrous heme b 595 induced by CO binding with heme d (23)). The slower part of recombination included 2-3 phases with values in the range of 0.2-2.3 ms, but the difference spectra of the phases were rather similar and indicated CO binding with a b-type heme in agreement with the findings in Ref.…”

Section: Room Temperature Static Spectra-mentioning

confidence: 99%

“…20 -22 and references therein). However, the spectral features attributed to CO binding with b 595 could be caused by a small bandshift of unligated heme b 595 induced by CO interaction with the nearby heme d (23). Moreover, magnetic circular dichroism spectroscopy has shown that only a small fraction of heme b 595 , if any, in the E. coli cytochrome bd binds CO or NO at room temperature.…”

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confidence: 99%

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Interaction of Cytochrome bd with Carbon Monoxide at Low and Room Temperatures

Borisov

Sedelnikova

Poole

et al. 2001

Journal of Biological Chemistry

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Azotobacter vinelandii is an obligately aerobic bacterium in which aerotolerant dinitrogen fixation requires cytochrome bd. This oxidase comprises two polypeptide subunits and three hemes, but no copper, and has been studied extensively. However, there remain apparently conflicting reports on the reactivity of the high spin heme b 595 with ligands. Using purified cytochrome bd, we show that absorption changes induced by CO photodissociation from the fully reduced cytochrome bd at low temperatures demonstrate binding of the ligand with heme b 595 . However, the magnitude of these changes corresponds to the reaction with CO of only about 5% of the heme. CO binding with a minor fraction of heme b 595 is also revealed at room temperature by time-resolved studies of CO recombination. The data resolve the apparent discrepancies between conclusions drawn from room and low temperature spectroscopic studies of the CO reaction with cytochrome bd. The results are consistent with the proposal that hemes b 595 and d form a diheme oxygen-reducing center with a binding capacity for a single exogenous ligand molecule that partitions between the hemes d and b 595 in accordance with their intrinsic affinities for the ligand. In this model, the affinity of heme b 595 for CO is about 20-fold lower than that of heme d.Cytochrome bd is a terminal oxidase present in the respiratory chains of many bacteria (reviewed in Ref. 1, see an evolutionary tree in Ref. 2). The enzyme catalyzes reduction of molecular oxygen to water by ubiquinol or menaquinol as natural electron donors (3-5) but shows no sequence homology to the heme-copper quinol oxidases. Also, in contrast to these oxidases, cytochrome bd does not contain copper and, although generating ⌬ (6 -9), does not pump protons (10).Cytochrome bd-type oxidases purified from Azotobacter vinelandii or Escherichia coli consist of two subunits and carry three iron-porphyrin groups: low spin heme b 558 , high spin heme b 595 , and a chlorin-type high spin iron-porphyrin group (heme d). All three redox centers are proposed to be located near the periplasmic side of the membrane (2). Heme b 558 is directly involved in ubiquinol oxidation (11,12). Heme d binds O 2 and is involved in the trapping and reduction of oxygen (3). The specific role of heme b 595 is still a matter of debate. One obvious possible role is the transferrence of electrons from heme b 558 to heme d (13-15). However, because heme b 595 is high spin, it is tempting to consider its involvement in dioxygen reduction; it was proposed that hemes b 595 and d might form a binuclear dioxygen reduction center analogous to the hemecopper oxygen-reducing site in the cytochrome aa 3 -or bo 3 -type oxidases (16 -19). In such a case, one might expect heme b 595 to react with other exogenous ligands such as CO or NO as is typical of most high spin hemoproteins. Surprisingly, despite a long history of such studies, this essential and apparently simple question has not been answered by the apparently conflicting data. The intricate line shape ...

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Section: Room Temperature Static Spectra-mentioning

confidence: 94%

mentioning

confidence: 89%

Section: Room Temperature Static Spectra-mentioning

confidence: 99%

mentioning

confidence: 99%

See 2 more Smart Citations

Interaction of Cytochrome bd with Carbon Monoxide at Low and Room Temperatures

Borisov

Sedelnikova

Poole

et al. 2001

Journal of Biological Chemistry

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“…However the role of high-spin heme b 595 is still a matter of debate. Together with heme d, heme b 595 is proposed to form a binuclear site for the effective reduction of oxygen analogous to the high-spin heme͞ Cu B binuclear center in the heme-copper oxidases (17)(18)(19)(20)(21)(22)(23). The electron transfer sequence in cytochrome bd is thought to be QH 2 3 b 558 3 [b 595 3 d] 3 O 2 (24)(25)(26).…”

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confidence: 99%