Investigations of the Efficient Electrocatalytic Interconversions of Carbon Dioxide and Carbon Monoxide by Nickel-Containing Carbon Monoxide Dehydrogenases - The Metal-Driven Biogeochemistry of Gaseous Compounds in the Environment - page 86

Figure 7 Chronoamperometric measurements of the inactivation (a and b) and re-activation
(c and d) rate of cyanide-inhibited CODH I Ch (c) and CODH II Ch (a, b, d). The inactivation rate of
CODH II Ch was measured at -460 mV (CO oxidation, (a)) and at -560 mV (CO 2 reduction, (b)). A
final concentration of 0.5 mM cyanide in the electrochemical cell was used to measure the half-life
time for inactivation. Cyanide release from CODH II Ch (d) at -760 mV is much faster than the
instrumental response. Conditions: 25 C, 0.2 M MES buffer (pH ¼ 7.0), and rotation rate
3500 rpm. Reproduced by permission from [ 19 ]; copyright 2013 Wiley-VCH Verlag GmbH &
Co. KGaA.
C red2 , the small overpotential reflecting the additional energy required to dislodge
the inhibitor by oxidation.
The binding and release of CN and NCO are orders of magnitude slower than
the catalytic turnover frequencies of their substrate counterparts CO and CO 2 , thus
showing that these analogues, while having very similar molecular shapes and size,
fall far short of being really good analogues [ 19 ]. The differences must ultimately
relate to acid-base (proton-transfer) properties, overall electrostatic effects and
subtle effects of frontier orbitals. Comparisons between CODH I Ch and CODH
II Ch show that rates of both inhibition by CN and re-activation are higher for
CODH II Ch even though it binds CN more tightly in a thermodynamic sense,
mirroring the stronger binding of CO that makes it such a potent product inhibitor of
this isozyme [ 19 ].