Azide Binding to Carbon Monoxide Dehydrogenase from Clostridium thermoaceticum

Mechanism of CO oxidation by carbon monoxide dehydrogenase from Clostridium thermoaceticum and its inhibition by anions

“…The relaxation properties (temperature and power dependence of the EPR signals) of the anion adducts are similar to those of center C and are very different from those of center A or B. (iii) The Ki values measured by EPR and UV-visible spectroscopic titrations are similar to the inhibition constant for the free enzyme-thiocyanate complex determined by steady-state kinetic experiments.4 (iv) The pH dependence of the EPR spectrum of center C matches those of CO oxidation and thiocyanate inhibition of this reaction, (v) Electron spin echo envelope modulation studies using l4N3 and ,5N3 demonstrate that azide nitrogens are directly coordinated to the center that gives rise to the 2.15 and 2.17 EPR signals (Kumar et al, 1995). It is surprising that anions that are noncompetitive inhibitors with relatively high K\ values have more marked effects on the EPR spectrum of center C than does cyanide which is a potent competitive inhibitor.…”

Nickel-Containing Carbon Monoxide Dehydrogenase/Acetyl-CoA Synthase,

“…EPR and resonance raman (RR) experiments have provided strong evidence that nickel is present and that there is a bridge between Ni and the Fe-S cluster components of cluster C. (i) EPR studies of the thiocyanate adduct of cluster C provided evidence that Ni is bridged to an iron site in the C cluster from C. thermoaceticum . The g values of the adduct are far from that of a [Fe 4 -S 4 ] 2+/1+ cluster and more closely resemble the spectra of paramagnetic Ni(I) complexes with a g av of ∼2.17 (Figure ). , However, the spectra show hyperfine broadening from substitution with 57 Fe and not 61 Ni. The unusual g values and the small 61 Ni coupling constant for the different states of cluster C were recently explained by assuming that a high-spin Ni(II) site is weakly coupled ( J ≈ 2 cm -1 ) to the S = 1 / 2 state of the [Fe 4 -S 4 ] 2+/1+ cluster .…”

“…Azide, thiocyanate, and cyanate also have been shown to bind to cluster C . They are very weak inhibitors of the enzyme and cause marked changes in the EPR spectrum of cluster C .…”

Structure, Function, and Mechanism of the Nickel Metalloenzymes, CO Dehydrogenase, and Acetyl-CoA Synthase

“…60b,67,69,71c,88,90,104 Here we will describe research on these inhibitors that has helped to enlighten the CODH catalytic mechanism.…”

“…Several molecules including nitrous oxide, sulfide, azide, thiocyanate, cyanate, cyanide, and n -BIC are known to inhibit the catalytic activity of CODHs. 60b , 67 , 69 , 71c , 88 , 90 , 104 Here we will describe research on these inhibitors that has helped to enlighten the CODH catalytic mechanism.…”