Leisinger T, Braus-Stromeyer S A
Mikrobiologisches Institut ETH, ETH-Zentrum Zürich, Switzerland.
Environ Health Perspect. 1995 Jun;103 Suppl 5(Suppl 5):33-6. doi: 10.1289/ehp.95103s433.
Chlorinated methanes are important industrial chemicals and significant environmental pollutants. While the highly chlorinated methanes, trichloromethane and tetrachloromethane, are not productively metabolized by bacteria, chloromethane and dichloromethane are used by both aerobic and anaerobic methylotrophic bacteria as carbon and energy sources. Some of the dehalogenation reactions involved in the utilization of the latter two compounds have been elucidated. In a strictly anaerobic acetogenic bacterium growing with chloromethane, an inducible enzyme forming methyltetrahydrofolate and chloride from chloromethane and tetrahydrofolate catalyzes dehalogenation of the growth substrate. A different mechanism for the nucleophilic displacement of chloride is observed in aerobic methylotrophic bacteria utilizing dichloromethane as the sole carbon and energy source. These organisms possess the enzyme dichloromethane dehalogenase which, in a glutathione-dependent reaction, converts dichloromethane to inorganic chloride and formaldehyde, a central metabolite of methylotrophic growth. Sequence comparisons have shown that bacterial dichloromethane dehalogenases belong to the glutathione S-transferase enzyme family, and within this family to class Theta. The dehalogenation reactions underlying aerobic utilization of chloromethane by a pure culture and anaerobic growth with dichloromethane by an acetogenic mixed culture are not known. It appears that they are based on mechanisms other than nucleophilic attack by tetrahydrofolate or glutathione.
氯代甲烷是重要的工业化学品和显著的环境污染物。虽然高氯代甲烷三氯甲烷和四氯化碳不能被细菌进行有效代谢，但氯甲烷和二氯甲烷可被需氧和厌氧甲基营养细菌用作碳源和能源。后两种化合物利用过程中涉及的一些脱卤反应已得到阐明。在以氯甲烷生长的严格厌氧产乙酸细菌中，一种可诱导的酶能将氯甲烷和四氢叶酸转化为甲基四氢叶酸和氯离子，催化生长底物的脱卤反应。在以二氯甲烷作为唯一碳源和能源的需氧甲基营养细菌中，观察到了氯离子亲核取代的不同机制。这些生物体拥有二氯甲烷脱卤酶，该酶在依赖谷胱甘肽的反应中，将二氯甲烷转化为无机氯和甲醛，甲醛是甲基营养生长的一种中心代谢物。序列比较表明，细菌二氯甲烷脱卤酶属于谷胱甘肽S -转移酶酶家族，且在该家族中属于Theta类。关于纯培养物对氯甲烷的需氧利用以及产乙酸混合培养物对二氯甲烷的厌氧生长所依据的脱卤反应尚不清楚。似乎它们基于除四氢叶酸或谷胱甘肽亲核攻击之外的其他机制。
