title: S-methylmethionine is both a substrate and an inactivator of 1-aminocyclopropane-1-carboxylate synthase.
abstract: S-methyl-L-methionine (SMM) is ubiquitous in the tissues of flowering plants, but its precise function remains unknown. It is both a substrate and an inhibitor of the pyridoxal 5(')-phosphate-dependent enzyme 1-aminocyclopropane-1-carboxylate (ACC) synthase, due to its structural similarity to the natural substrate of this enzyme, S-adenosyl-L-methionine. In the reaction with ACC synthase, SMM can either be transaminated to yield 4-dimethylsulfonium-2-oxobutyrate; converted to alpha-ketobutyrate, ammonia, and dimethylsulfide; or inactivate the enzyme covalently after elimination of dimethylsulfide. These results suggest a previously unrecognized role for SMM in the regulation of ACC synthase activity in plants.
authors.affiliation: Department of Chemistry, University of California, 239 A Hildebrand Hall 3206, Berkeley, CA 94720-3206, USA.
authors.forename: SaeHee
authors.initials: S
authors.lastname: Ko
authors.forename: Andrew C
authors.initials: AC
authors.lastname: Eliot
authors.forename: Jack F
authors.initials: JF
authors.lastname: Kirsch
mesh_terms: D002384:Catalysis; D004791:Enzyme Inhibitors / Q000378:metabolism / Q000494:pharmacology; D005470:Fluorometry; D007700:Kinetics; D008190:Lyases / Q000037:antagonists & inhibitors* / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D010084:Oxidation-Reduction; D010843:Pichia / Q000201:enzymology; D013379:Substrate Specificity; D000637:Transaminases / Q000378:metabolism; D014814:Vitamin U / Q000378:metabolism* / Q000494:pharmacology*
chemical_list: D004791:Enzyme Inhibitors; D014814:Vitamin U; D000637:Transaminases; D008190:Lyases; C021773:1-aminocyclopropanecarboxylate synthase