Involved in the synthesis of autoinducer 2 (AI-2) which is secreted by bacteria and is used to communicate both the cell density and the metabolic potential of the environment. The regulation of gene expression in response to changes in cell density is called quorum sensing. Catalyzes the transformation of S-ribosylhomocysteine (RHC) to homocysteine (HC) and 4,5-dihydroxy-2,3-pentadione (DPD) (By similarity). S-(5-deoxy-D-ribos-5-yl)-L-homocysteine = (S)-4,5-dihydroxypentane-2,3-dione + L-homocysteine Binds 1 Fe cation per subunit. Homodimer. Expression is growth phase-dependent, with maximal expression in the mid-exponential growth phase. Induced by high salt concentrations (at protein level). Belongs to the LuxS family.