title: Effect of sodium sulfide on Ni-containing carbon monoxide dehydrogenases.
abstract: The structure of the active-site C-cluster in CO dehydrogenase from Carboxydothermus hydrogenoformans includes a mu(2)-sulfide ion bridged to the Ni and unique Fe, whereas 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 microM 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 toward attacking Ni-bound carbonyl.
authors.affiliation: Department of Chemistry, Texas A&M University, College Station, 77843-3255, USA.
authors.forename: Jian
authors.initials: J
authors.lastname: Feng
authors.forename: Paul A
authors.initials: PA
authors.lastname: Lindahl
mesh_terms: D000445:Aldehyde Oxidoreductases / Q000037:antagonists & inhibitors / Q000737:chemistry* / Q000378:metabolism; D002248:Carbon Monoxide / Q000737:chemistry / Q000378:metabolism; D004578:Electron Spin Resonance Spectroscopy; D006094:Gram-Positive Bacteria / Q000201:enzymology; D007700:Kinetics; D009097:Multienzyme Complexes / Q000037:antagonists & inhibitors / Q000737:chemistry* / Q000378:metabolism; D009532:Nickel / Q000737:chemistry / Q000378:metabolism; D010084:Oxidation-Reduction; D012247:Rhodospirillum rubrum / Q000201:enzymology; D013440:Sulfides / Q000737:chemistry* / Q000378:metabolism / Q000494:pharmacology
chemical_list: D009097:Multienzyme Complexes; D013440:Sulfides; D009532:Nickel; D002248:Carbon Monoxide; D000445:Aldehyde Oxidoreductases; C019823:carbon monoxide dehydrogenase; C033479:sodium sulfide