Diekert G B, Thauer R K
J Bacteriol. 1978 Nov;136(2):597-606. doi: 10.1128/jb.136.2.597-606.1978.
Cultures of Clostridium formicoaceticum and C. thermoaceticum growing on fructose and glucose, respectively, were shown to rapidly oxidize CO to CO(2). Rates up to 0.4 mumol min(-1) mg of wet cells(-1) were observed. Carbon monoxide oxidation by cell suspensions was found (i) to be dependent on pyruvate, (ii) to be inhibited by alkyl halides and arsenate, and (iii) to stimulate CO(2) reduction to acetate. Cell extracts catalyzed the oxidation of carbon monoxide with methyl viologen at specific rates up to 10 mumol min(-1) mg of protein(-1) (35 degrees C, pH 7.2). Nicotinamide adenine dinucleotide, nicotinamide adenine dinucleotide phosphate and ferredoxin from C. pasteurianum were ineffective as electron acceptors. The catalytic mechanism of carbon monoxide oxidation was "ping-pong," indicating that the enzyme catalyzing carbon monoxide oxidation can be present in an oxidized and a reduced form. The oxidized form was shown to react reversibly with cyanide, and the reduced form was shown to react reversibly with alkyl halides: cyanide inactivated the enzyme only in the absence of carbon monoxide, and alkyl halides inactivated it only in the presence of carbon monoxide. Extracts inactivated by alkyl halides were reactivated by photolysis. The findings are interpreted to indicate that carbon monoxide oxidation in the two bacteria is catalyzed by a corrinoid enzyme and that in vivo the reaction is coupled with the reduction of CO(2) to acetate. Cultures of C. acidi-urici and C. cylindrosporum growing on hypoxanthine were found not to oxidize CO, indicating that clostridia mediating a corrinoid-independent total synthesis of acetate from CO(2) do not possess a CO-oxidizing system.
分别以果糖和葡萄糖为生长底物的甲酸乙酸梭菌和热乙酸梭菌培养物被证明能迅速将CO氧化为CO₂。观察到的速率高达0.4 μmol min⁻¹ mg湿细胞⁻¹。发现细胞悬液对一氧化碳的氧化作用：(i) 依赖于丙酮酸，(ii) 受卤代烷和砷酸盐抑制，(iii) 能刺激CO₂还原为乙酸盐。细胞提取物以高达10 μmol min⁻¹ mg蛋白质⁻¹的比速率（35℃，pH 7.2）催化一氧化碳与甲基紫精的氧化反应。来自巴氏梭菌的烟酰胺腺嘌呤二核苷酸、烟酰胺腺嘌呤二核苷酸磷酸和铁氧化还原蛋白作为电子受体无效。一氧化碳氧化的催化机制为“乒乓”机制，表明催化一氧化碳氧化的酶可以以氧化态和还原态存在。氧化态显示与氰化物可逆反应，还原态显示与卤代烷可逆反应：氰化物仅在没有一氧化碳的情况下使酶失活，卤代烷仅在有一氧化碳的情况下使酶失活。被卤代烷灭活的提取物通过光解重新激活。这些发现被解释为表明这两种细菌中的一氧化碳氧化是由一种类咕啉酶催化的，并且在内体中该反应与CO₂还原为乙酸盐相偶联。发现以次黄嘌呤为生长底物的尿酸梭菌和柱状芽孢梭菌培养物不氧化CO，这表明介导从CO₂进行不依赖类咕啉的乙酸盐全合成的梭菌不具有CO氧化系统。
