Owing to their importance, diversity and abundance of generated paramagnetic species, radical S-adenosylmethionine (rSAM) enzymes have become popular targets for electron paramagnetic resonance (EPR) spectroscopic studies. In contrast to prototypic single-domain and thus single-[4Fe–4S]-containing rSAM enzymes, there is a large subfamily of rSAM enzymes with multiple domains and one or two additional iron–sulfur cluster(s) called the SPASM/twitch domain-containing rSAM enzymes. EPR spectroscopy is a powerful tool that allows for the observation of the iron–sulfur clusters as well as potentially trappable paramagnetic reaction intermediates. Here, we review continuous-wave and pulse EPR spectroscopic studies of SPASM/twitch domain-containing rSAM enzymes. Among these enzymes, we will review in greater depth four well-studied enzymes, BtrN, MoaA, PqqE, and SuiB. Towards establishing a functional consensus of the additional architecture in these enzymes, we describe the commonalities between these enzymes as observed by EPR spectroscopy.

由于它们的重要性、多样性和生成的顺磁性物质的丰富性，自由基S-腺苷甲硫氨酸 (rSAM) 酶已成为电子顺磁共振 (EPR) 光谱研究的热门目标。与原型单结构域和因此含有单个 [4Fe-4S] 的 rSAM 酶相比，有一个大型 rSAM 酶亚家族，具有多个结构域和一个或两个额外的铁硫簇，称为 SPASM/twitch 结构域-含有rSAM酶。EPR 光谱是一种强大的工具，可以观察铁硫簇以及可能捕获的顺磁性反应中间体。在这里，我们回顾了包含 rSAM 酶的 SPASM/twitch 域的连续波和脉冲 EPR 光谱研究。在这些酶中，我们将更深入地回顾四种经过充分研究的酶，BtrN、MoaA、PqqE 和 SuiB。