Carbon monoxide dehydrogenase from Rhodospirillum rubrum: effect of redox potential on catalysis.
Carbon monoxide dehydrogenase from Rhodospirillum rubrum: effect of redox potential on catalysis.
复制标题
红色红螺菌的一氧化碳脱氢酶：氧化还原电位对催化的影响。
DOI：
10.1021/bi0357199
复制
发表时间：
2004
期刊：
影响因子：
2.9
通讯作者：
Lindahl,PaulA
中科院分区：
文献类型：
--
作者：
Feng,Jian;Lindahl,PaulA
The Ni−Fe−S-containing C-cluster of carbon monoxide dehydrogenases is the active site for catalyzing the reversible oxidation of CO to CO2. This cluster can be stabilized in redox states designated Cox, Cred1, Cint, and Cred2. What had until recently been the best-supported mechanism of catalysis involves a one-electron reductive activation of Coxto Cred1and a catalytic cycle in which the Cred1state binds and oxidizes CO, forming Cred2and releasing CO2. Recent experiments cast doubt on this mechanism, as they imply that activation requires reducing the C-cluster to a state more reduced than Cred1. In the current study, redox titration and stopped-flow kinetic experiments were performed to assess the previous results and conclusions. Problems in previous methods were identified, and related experiments for which such problems were eliminated or minimized afforded significantly different results. In contrast to the previous study, activation did not correlate with reduction of Fe−S clusters in the enzyme, suggesting that the potential required for activation was milder than that required to reduce these clusters (i.e.,E0act> −420 mV vs SHE). Using enzyme preactivated in solutions that were poised at various potentials, lag phases were observed prior to reaching steady-state CO oxidation activities. Fits of the Nernst equation to the corresponding lag-vs-potential plot yielded a midpoint potential of −150 ± 50 mV. This value probably reflectsE°‘ for the Cox/Cred1couple, and it suggests that Cred1is indeed active in catalysis.
