S-Ribosylhomocysteinase (LuxS) catalyzes the cleavage of the thioether bond in S-ribosylhomocysteine to produce L- homocysteine and 4,5-dihydroxy-2,3-pentanedione, the precursor of type II bacterial quorum sensing autoinducer. This work carried out extensive mechanistic studies of the LuxS reaction. The native metal cofactor of LuxS was identified as ferrous ion, instead of previously reported zinc ion, with a potential catalytic role. Substantial evidence was provided for the internal redox reaction, which comprised two consecutive carbonyl migration steps followed by -elimination. Three...