Catalyzes the addition of fumarate to the methyl group of toluene, leading to the formation of benzylsuccinate. fumarate + toluene = 2-benzylsuccinate Activated by the benzylsuccinate synthase activating enzyme BssD. Rapidly inactivated by oxygen. Optimum pH is 8.0. Xenobiotic degradation; toluene degradation. Heterohexamer composed of 2 alpha subunits, 2 beta subunits and 2 gamma subunits. Induced by toluene, probably via the TdiR/TdiS two-component regulatory system.