Organization of Clusters and Internal Electron Pathways in CO Dehydrogenase from Clostridium thermoaceticum: Relevance to the Mechanism of Catalysis and Cyanide Inhibition

Anderson, Mark E.; Lindahl, Paul A.

doi:10.1021/bi00195a011

Cited by 66 publications

(136 citation statements)

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“…The effect of sulfide ion on CODH activity and spectral properties are qualitatively similar to those of other anions, including cyanide, cyanate, thiocyanate, and azide ions (15)(16)(17). Cyanide ion fully inhibits CODH's, apparently by binding to the C red1 state as evidenced by a shift in the C red1 EPR signal when CN -is added (15).…”

Section: Discussionmentioning

confidence: 62%

“…Cyanide ion fully inhibits CODH's, apparently by binding to the C red1 state as evidenced by a shift in the C red1 EPR signal when CN -is added (15). This effect can be reversed (i.e.…”

Section: Discussionmentioning

confidence: 99%

“…With CN -bound, added CO cannot reduce the enzyme's Fe-S clusters, suggesting that CO does not oxidize to CO 2 when CN -is bound. Nevertheless, CO incubation can (somehow) accelerate the dissociation of CN - (15). One possibility is that CO binds to the Ccluster in the C red1 state with CN -bound simultaneously, and that this binding encourages CNdissociation (15,18).…”

Section: Discussionmentioning

confidence: 99%

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Effect of Sodium Sulfide on Ni-Containing Carbon Monoxide Dehydrogenases

Feng

Lindahl

2004

J. Am. Chem. Soc.

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Running Title: Effect of Sulfide on CODH 2 AbstractThe structure of the active-site C-cluster in CO dehydrogenase from Carboxythermus hydrogenoformans includes a µ 2 -sulfide ion bridged to the Ni and unique Fe, while the same cluster in enzymes from Rhodospirillum rubrum (CODH Rr ) and Moorella thermoacetica (CODH Mt ) lack this ion. This difference was investigated by exploring the effects of sodium sulfide on activity and spectral properties. Sulfide partially inhibited the CO oxidation activity of CODH Rr and generated a lag prior to steady-state. CODH Mt was inhibited similarly but without a lag. Adding sulfide to CODH Mt in the C red1 state caused the g av = 1.82 EPR signal to decline and new features to appear, including one with g = 1.95, 1.85 and (1.70 or 1.62). Removing sulfide caused the g av = 1.82 signal to reappear and activity to recover. Sulfide did not affect the g av = 1.86 signal from the C red2 state. A model was developed in which sulfide binds reversibly to C red1 , inhibiting catalysis. Reducing this adduct causes sulfide to dissociate, C red2 to develop, and activity to recover. Using this model, apparent K I values are 40 ± 10 nM for CODH Rr and 60 ± 30 µM for CODH Mt . Effects of sulfide are analogous to those of other anions, including the substrate hydroxyl group, suggesting that these ions also bridge the Ni and unique Fe. This proposed arrangement raises the possibility that CO binding labilizes the bridging hydroxyl and increases its nucleophilic tendency towards attacking Ni-bound carbonyl.3 Ni-containing carbon monoxide dehydrogenases are found in anaerobic bacteria and archaea that grow autotrophically on CO or CO 2 and reducing equivalents (1). There are other potentially important differences between these structures but these will not be discussed here.The C-cluster can be stabilized in four redox states, called C ox , C red1 , C int and C red2 (6-9).The fully-oxidized C ox state is S = 0 and appears not to be involved in CO/CO 2 redox catalysis. 4 Reduction by 1 electron to the S = ½ C red1 state activates the enzyme (10). During catalysis, CO probably coordinates to the Ni of the C-cluster in this state, followed by the attack of the carbonyl by a hydroxide ion, forming a Ni-bound carboxylate. The S = ½ C red2 state then forms as CO 2 dissociates. The C-cluster in the C red2 state transfers 2 electrons, in 1-electron steps, to the B-and D-clusters. In doing so, it passes through an EPR-silent C int state (9) and ultimately returns to the C red1 state (7).We were intrigued by the µ 2 -sulfide ion uniquely found in the CODH Ch C-cluster, and endeavored to understand the circumstances for its presence. One possibility was that this sulfide ion is required for catalysis and that the 3 structures lacking it might reflect enzyme crystallized in an inactive form. Alternatively, the sulfide ion might inhibit catalysis and CODH Ch might have been crystallized in an inactive form. Other possibilities are that the C-cluster in CODH Ch might differ intrinsically from those in the othe...

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Section: Discussionmentioning

confidence: 62%

“…Cyanide ion fully inhibits CODH's, apparently by binding to the C red1 state as evidenced by a shift in the C red1 EPR signal when CN -is added (15). This effect can be reversed (i.e.…”

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

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Effect of Sodium Sulfide on Ni-Containing Carbon Monoxide Dehydrogenases

Feng

Lindahl

2004

J. Am. Chem. Soc.

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“…At potentials below -200 mV, diamagnetic C ox is reduced by 1 electron to the S = ½ C red1 state exhibiting an EPR signal with g av = 1.82 (18,26 (14,16,27).…”

Section: Redox and Spectroscopic Properties Of B-and D-clustersmentioning

confidence: 99%

The Ni-Containing Carbon Monoxide Dehydrogenase Family: Light at the End of the Tunnel?

2002

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“…The B and C clusters are located in the ␤ subunit, whereas the A cluster is located in ␣. The B cluster is a standard [Fe 4 S 4 ] 2ϩ/1ϩ cluster involved in electron transfer (4), and it exhibits an EPR signal with g av ϭ 1.94 when reduced to the B red state (5). The C cluster is the active site for CO 2 ͞CO redox catalysis (6)(7)(8)(9) and likely consists of an Ni complex weakly coupled through an unidentified bridge to an Fe 4 S 4 cluster (10,11).…”

mentioning

confidence: 99%