Quinone specificity for electron donors and terminal acceptors. E. coli iJR904 also accounts for the quinone specificity of different reactions. Electron donors are listed on the left, terminal electron acceptors are on the right, and the three types of quinones (DMK, MK, Q; note that these abbreviations differ from those listed in the additional data files) that serve as carriers are shown in the middle. The electron donors shown in red were able to donate their electrons to fumarate in iJE660a, but are now unable to do so. DMK, demethylmenaquinone; DMSO, dimethyl sulfoxide; MK, menaquinone; Q, ubiquinone; TMAO, trimethylamine N-oxide.