Benzylsuccinate synthase belongs to the family of fumarate-adding enzymes (FAE) which is itself part of the growing superfamily of glycyl radical enzymes (GRE) . GRE are involved in surprisingly different, but always chemically demanding reactions in anaerobic metabolic pathways of Bacteria, Archaea, and Eukarya. In addition to FAE, the currently known families of GRE consist of the pyruvate formate lyases (PFL) , type III anaerobic ribonucleotide reductases (ARNR) , glycerol or diol dehydratases ,