Environmental Engineering Reference
In-Depth Information
5.1 How Class IV Carbon Monoxide Dehydrogenases
Respond to Cyanide
Qualitative details of the enzyme's inhibition by cyanide are revealed in the cyclic
voltammograms shown in Figure 6 , which were recorded for CODH I Ch and CODH
II Ch [ 18 , 19 ]. A complication here is that cyanide is lost quite rapidly from
the electrochemical cell as HCN, but key characteristics are easily seen and
extracted. The important observations are summarized as follows. When CN is
Figure 6 A potential-domain dynamic picture of the effect of cyanide on catalytic properties of
CODH. Left panels: Inhibition of CO oxidation activity of CODH I Ch and CODH II Ch by cyanide
under 100 % CO. An aliquot of KCN stock solution (giving a final concentration of 1 mM in the
electrochemical cell) was injected during the second cycle. Conditions: 25 C, 0.2 M MES buffer
(pH ¼ 7.0), electrode rotation rate, 3500 rpm, scan rate, 1 mV sec 1 . Right panels: Inhibition of
CO 2 reduction activity of CODH I Ch and CODH II Ch by CN under 100 % CO 2 , showing that CN
does not bind under strongly reducing conditions. An aliquot of KCN stock solution (giving a final
concentration of 1 mM in the electrochemical cell) was injected during the second cycle. Note that
a more negative potential (by approximately 70 mV) is required to reductively reactivate CODH
II Ch . Conditions: 25 C, 0.2 MMES buffer (pH ¼ 7.0), electrode rotation rate, 3500 rpm, scan rate,
1 mV sec 1 . Reproduced by permission from [ 19 ]; copyright 2013 Wiley-VCH Verlag GmbH &
Co. KGaA.
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