Activation of benzylsuccinate synthase under anaerobic conditions by generation of an organic free radical, using S-adenosylmethionine and reduced flavodoxin as cosubstrates to produce 5'-deoxy-adenosine. 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. Xenobiotic degradation; toluene degradation [regulation]. Induced by toluene, probably via the TdiR/TdiS two-component regulatory system. Belongs to the organic radical-activating enzymes family.