Cysteine S-conjugate beta-lyases.
Cysteine S-conjugate beta-lyases are pyridoxal 5'-phosphate-containing enzymes that catalyze beta-elimination reactions with cysteine S-conjugates that possess an electron-withdrawing group attached at the sulfur. The end products of the beta-lyase reaction are pyruvate, ammonium and a sulfur-containing fragment. If the sulfur-containing fragment is reactive, the parent cysteine S-conjugate may be toxic, particularly to kidney mitochondria. Halogenated alkenes are examples of electrophiles that are bioactivated (toxified) by conversion to cysteine S-conjugates. These conjugates are converted by cysteine S-conjugate beta-lyases to thioacylating fragments. Several cysteine S-conjugates found in allium foods (garlic and onion) are beta-lyase substrates. This finding may account in part for the chemopreventive activity of allium products. This review (1) identifies enzymes that catalyze cysteine S-conjugate beta-lyase reactions, (2) suggests that toxicant channeling may contribute to halogenated cysteine S-conjugate-induced toxicity to mitochondria, and (3) proposes mechanisms that may contribute to the antiproliferative effects of sulfur-containing fragments eliminated from allium-derived cysteine S-conjugates.
Cooper
A J L
AJ
Department of Biochemistry, Weill Medical College, Cornell University, New York, New York, USA. acooper@burke.org
Pinto
J T
JT
D000818:Animals; D013437:Carbon-Sulfur Lyases / Q000378:metabolism*; D005737:Garlic / Q000378:metabolism; D006801:Humans; D006846:Hydrocarbons, Halogenated / Q000378:metabolism / Q000633:toxicity; D008322:Mammals; D050217:Metabolic Detoxication, Phase II; D008928:Mitochondria / Q000187:drug effects / Q000378:metabolism; D008954:Models, Biological; D011355:Prodrugs / Q000378:metabolism
D006846:Hydrocarbons, Halogenated; D011355:Prodrugs; D013437:Carbon-Sulfur Lyases; C019969:S-alkylcysteine lyase