Buckel Wolfgang, Golding Bernard T
Fachbereich Biologie, Philipps-Universität, D-35032 Marburg, Germany.
Annu Rev Microbiol. 2006;60:27-49. doi: 10.1146/annurev.micro.60.080805.142216.
This review describes enzymes that contain radicals and/or catalyze reactions with radical intermediates. Because radicals irreversibly react with dioxygen, most of these enzymes occur in anaerobic bacteria and archaea. Exceptions are the families of coenzyme B(12)- and S-adenosylmethionine (SAM)-dependent radical enzymes, of which some members also occur in aerobes. Especially oxygen-sensitive radical enzymes are the glycyl radical enzymes and 2-hydroxyacyl-CoA dehydratases. The latter are activated by an ATP-dependent one-electron transfer and act via a ketyl radical anion mechanism. Related enzymes are the ATP-dependent benzoyl-CoA reductase and the ATP-independent 4-hydroxybenzoyl-CoA reductase. Ketyl radical anions may also be generated by one-electron oxidation as shown by the flavin-adenine-dinucleotide (FAD)- and [4Fe-4S]-containing 4-hydroxybutyryl-CoA dehydratase. Finally, two radical enzymes are discussed, pyruvate:ferredoxin oxidoreductase and methane-forming methyl-CoM reductase, which catalyze their main reaction in two-electron steps, but subsequent electron transfers proceed via radicals.
本综述描述了含有自由基和/或催化涉及自由基中间体反应的酶。由于自由基会与氧气发生不可逆反应，这些酶大多存在于厌氧细菌和古细菌中。例外的是依赖辅酶B12和S-腺苷甲硫氨酸（SAM）的自由基酶家族，其中一些成员也存在于需氧生物中。对氧气特别敏感的自由基酶是甘氨酰自由基酶和2-羟基酰基辅酶A脱水酶。后者通过依赖ATP的单电子转移被激活，并通过酮基自由基阴离子机制起作用。相关的酶是依赖ATP的苯甲酰辅酶A还原酶和不依赖ATP的4-羟基苯甲酰辅酶A还原酶。如含有黄素腺嘌呤二核苷酸（FAD）和[4Fe-4S]的4-羟基丁酰辅酶A脱水酶所示，酮基自由基阴离子也可能通过单电子氧化产生。最后，讨论了两种自由基酶，丙酮酸：铁氧化还原蛋白氧化还原酶和产甲烷的甲基辅酶M还原酶，它们在两电子步骤中催化其主要反应，但随后的电子转移通过自由基进行。
