title: Salmonella typhimurium LT2 catabolizes propionate via the 2-methylcitric acid cycle.
abstract: We previously identified the prpBCDE operon, which encodes catabolic functions required for propionate catabolism in Salmonella typhimurium. Results from (13)C-labeling experiments have identified the route of propionate breakdown and determined the biochemical role of each Prp enzyme in this pathway. The identification of catabolites accumulating in wild-type and mutant strains was consistent with propionate breakdown through the 2-methylcitric acid cycle. Our experiments demonstrate that the alpha-carbon of propionate is oxidized to yield pyruvate. The reactions are catalyzed by propionyl coenzyme A (propionyl-CoA) synthetase (PrpE), 2-methylcitrate synthase (PrpC), 2-methylcitrate dehydratase (probably PrpD), 2-methylisocitrate hydratase (probably PrpD), and 2-methylisocitrate lyase (PrpB). In support of this conclusion, the PrpC enzyme was purified to homogeneity and shown to have 2-methylcitrate synthase activity in vitro. (1)H nuclear magnetic resonance spectroscopy and negative-ion electrospray ionization mass spectrometry identified 2-methylcitrate as the product of the PrpC reaction. Although PrpC could use acetyl-CoA as a substrate to synthesize citrate, kinetic analysis demonstrated that propionyl-CoA is the preferred substrate.
authors.affiliation: Department of Bacteriology, University of Wisconsin-Madison, Madison, Wisconsin 53706-1567, USA.
authors.forename: A R
authors.initials: AR
authors.lastname: Horswill
authors.forename: J C
authors.initials: JC
authors.lastname: Escalante-Semerena
mesh_terms: D002247:Carbon Isotopes; D002950:Citrate (si)-Synthase / Q000378:metabolism; D002951:Citrates / Q000378:metabolism; D005838:Genotype; D007523:Isocitrates / Q000378:metabolism; D007700:Kinetics; D009682:Magnetic Resonance Spectroscopy; D013058:Mass Spectrometry; D008956:Models, Chemical; D009876:Operon; D007652:Oxo-Acid-Lyases / Q000378:metabolism; D011422:Propionates / Q000378:metabolism*; D012486:Salmonella typhimurium / Q000235:genetics / Q000378:metabolism*
chemical_list: D002247:Carbon Isotopes; D002951:Citrates; D007523:Isocitrates; D011422:Propionates; C021058:threo-alpha-methylisocitrate; C031605:2-methylcitric acid; D002950:Citrate (si)-Synthase; C112399:2-methylcitrate synthase; D007652:Oxo-Acid-Lyases