Anderson M E, Lindahl P A
Department of Chemistry, Texas A&M University, College Station 77843.
Biochemistry. 1994 Jul 26;33(29):8702-11. doi: 10.1021/bi00195a011.
Cyanide inhibits the CO oxidation activity of carbon monoxide dehydrogenase from Clostridium thermoaceticum by binding tightly to the form of the C-cluster yielding the gav = 1.82 signal (the C1.82 form). CN- dissociates and the enzyme reactivates upon addition of CO, CO2 plus dithionite, or CS2 plus dithionite. Dithionite slows the inhibition of the enzyme by CN-, but it cannot reactivate the enzyme. This behavior is explained by assuming that binding of CO, CO2, or CS2 at a modulator site accelerates the dissociation of CN- from the C-cluster. With CN- bound at the C-cluster, dithionite, but not CO, can reduce those Fe-S clusters in the enzyme whose redox status can be monitored at 420 nm. The electron pathway used for CO oxidation appears to be as follows: C-cluster-->Fe-S Clusters-->external electron acceptors. The electron used to reduce the NiFe complex originates predominantly from the C-cluster, and this reduction is inhibited when CN- is bound at the C-cluster. The NiFe complex is reduced more slowly (in the absence of CN-) than CO is catalytically oxidized, indicating that this reduction is not part of the catalytic mechanism for CO oxidation. The form of the C-cluster yielding the g(av) = 1.86 signal (C1.86) is proposed to be two electrons more reduced than C1.82 and able to bind and reduce CO2. CO is proposed to be oxidized by C1.82. Neither CO or CN- appears to bind C1.86.
氰化物通过与产生gav = 1.82信号的C簇形式（C1.82形式）紧密结合，抑制了来自热醋酸梭菌的一氧化碳脱氢酶的CO氧化活性。加入CO、CO2加连二亚硫酸盐或CS2加连二亚硫酸盐后，CN-解离且酶重新激活。连二亚硫酸盐减缓了CN-对酶的抑制作用，但不能使酶重新激活。这种行为可通过假设CO、CO2或CS2在调节位点的结合加速了CN-从C簇的解离来解释。当CN-结合在C簇上时，连二亚硫酸盐而非CO能够还原酶中那些氧化还原状态可在420 nm监测的铁硫簇。用于CO氧化的电子途径似乎如下：C簇→铁硫簇→外部电子受体。用于还原NiFe复合物的电子主要源自C簇，当CN-结合在C簇上时，这种还原受到抑制。NiFe复合物的还原比CO的催化氧化更慢（在不存在CN-的情况下），表明这种还原不是CO氧化催化机制的一部分。产生g(av) = 1.86信号的C簇形式（C1.86）被认为比C1.82多两个电子被还原，并且能够结合和还原CO2。CO被认为是由C1.82氧化的。CO或CN-似乎都不与C1.86结合。
