S ribosylhomocysteine lyase

In enzymology, a S-ribosylhomocysteine lyase (EC 4.4.1.21) is an enzyme that catalyzes the chemical reaction

Hence, this enzyme has one substrate, S-(5-deoxy-D-ribos-5-yl)-L-homocysteine, and two products, L-homocysteine and (4S)-4,5-dihydroxypentan-2,3-dione.

This enzyme belongs to the family of lyases, specifically the class of carbon-sulfur lyases. The systematic name of this enzyme class is S-(5-deoxy-D-ribos-5-yl)-L-homocysteine L-homocysteine-lyase [(4S)-4,5-dihydroxypentan-2,3-dione-forming]. Other names in common use include S-ribosylhomocysteinase, and LuxS. This enzyme participates in methionine metabolism.

Furthermore, LuxS is involved in the synthesis of autoinducer AI-2 (autoinducer-2), which is plays a role in quorum sensing in a certain number of bacterial species. LuxS converts S-ribosylhomocysteine to homocysteine and 4,5-dihydroxy-2,3-pentanedione (DPD); DPD can then spontaneously cyclisize to active AI-2. AI-2 is a signalling molecule that is believed to act in interspecies communication by regulating niche-specific genes with diverse functions in various bacteria, often in response to population density. However, an unequivocally AI-2 related behavior was found to be restricted primarily to bacteria bearing known AI-2 receptor genes. Thus, while it is certainly true that some bacteria can respond to AI-2, it is doubtful that it is always being produced for purposes of signalling. LuxS is a homodimeric iron-dependent metalloenzyme containing two identical tetrahedral metal-binding sites similar to those found in peptidases and amidases.