Booker Squire J
Department of Chemistry, The Pennsylvania State University, University Park, 16802, United States.
Curr Opin Chem Biol. 2009 Feb;13(1):58-73. doi: 10.1016/j.cbpa.2009.02.036. Epub 2009 Mar 16.
The functionalization of alkanes was once thought to lie strictly within the domain of enzymes that activate dioxygen in order to generate an oxidant with suitable potency to cleave inert C-H bonds. The emergence of the radical SAM superfamily of enzymes-those which use S-adenosyl-l-methionine as a precursor to a 5'-deoxyadenosyl 5'-radical-has kindled a renaissance in the study of radical-dependent enzymatic reactions, and is ushering in a wealth of new and intriguing chemistry that remains to be elucidated. This review will focus on a special subclass of radical SAM enzymes that functionalize inert C-H bonds, highlighting the functional groups and the chemistry that leads to their insertion. Within this class are first, enzymes that catalyze sulfur insertion, the prototype of which is biotin synthase; second, enzymes that catalyze P-methylation or C-methylation, such as P-methylase or Fom3; third, enzymes that catalyze oxygen insertion, such as the anaerobic magnesium protoporphyrin-IX oxidative cyclase (BchE); and fourth, enzymes that functionalize n-hexane or other alkanes as the first step in the metabolism of these inert compounds by certain bacteria. In addition to surveying reactions that have been studied at various levels of detail, this review will speculate on the mechanisms of other types of reactions that this chemistry lends itself to.
烷烃的官能团化曾被认为严格局限于激活双加氧以生成具有适当强度来裂解惰性碳氢键的氧化剂的酶的领域。自由基S-腺苷甲硫氨酸超家族的酶（即那些使用S-腺苷-L-甲硫氨酸作为5'-脱氧腺苷5'-自由基前体的酶）的出现，引发了对自由基依赖性酶促反应研究的复兴，并带来了大量有待阐明的新颖有趣的化学现象。本综述将聚焦于使惰性碳氢键官能团化的自由基S-腺苷甲硫氨酸酶的一个特殊亚类，突出导致其插入的官能团和化学反应。在这一类中，首先是催化硫插入的酶，其原型是生物素合酶；其次是催化磷甲基化或碳甲基化的酶，如磷甲基化酶或Fom3；第三是催化氧插入的酶，如厌氧镁原卟啉-IX氧化环化酶（BchE）；第四是使正己烷或其他烷烃官能团化的酶，这是某些细菌代谢这些惰性化合物的第一步。除了概述已在不同详细程度上研究过的反应外，本综述还将推测这种化学可能引发的其他类型反应的机制。
