Involved in an anaerobic respiration pathway that converts the sulfonate isethionate (2-hydroxyethanesulfonate) to ammonia, acetate and sulfide. Catalyzes activation of the isethionate sulfite-lyase IslA under anaerobic conditions by generation of an organic free radical on a glycine residue, via a homolytic cleavage of S-adenosyl-L-methionine (SAM). glycyl-[protein] + reduced [flavodoxin] + S-adenosyl-L-methionine = 5'-deoxyadenosine + glycin-2-yl radical-[protein] + H(+) + L-methionine + semiquinone [flavodoxin] Binds 3 [4Fe-4S] clusters. One cluster is coordinated with 3 cysteines and an exchangeable S-adenosyl-L-methionine. Organosulfur degradation; alkanesulfonate degradation. Monomer. Highly up-regulated in the presence of isethionate. Cells lacking this gene lose the ability to grow with isethionate as the terminal electron acceptor. Belongs to the organic radical-activating enzymes family.