title: Mechanism of action of butyryl-CoA dehydrogenase: reactions with acetylenic, olefinic, and fluorinated substrate analogues.
abstract: The acetylenic thio ester (3-pentynoyl)pantetheine irreversibly inactivates butyryl-CoA dehydrogenase from Megasphaera elsdenii. The inactivator becomes covalently attached to the protein (0.61 +/- 0.1 mol of 14C-labeled inactivator/mol of enzyme flavin). No modification of the flavin cofactor is seen. The covalent enzyme-inactivator adduct is labile toward base and neutral hydroxylamine. These treatments release 85 +/- 5% of the incorporated 14C label from the protein. Base-catalyzed hydrolysis of the adduct releases 3-oxopentanoic acid (0.6 mol/mol of incorporated inactivator). Treatment with hydroxylamine leads to formation of a hydroxamic acid on the protein (0.64 +/- 0.09 mol/mol of incorporated inactivator). The covalent adduct can be reduced with sodium borohydride with release of 1,3-pentanediol. Hydrolysis of the protein with 6 N HCl after sodium borohydride reduction yields 2-amino-5-hydroxyvaleric acid and proline. We conclude that the inactivator has reacted with the gamma-carboxyl group of a glutamate residue at the enzyme active site. The inactivation proceeds through enzyme-catalyzed rearrangement of the acetylene to an allene, followed by nucleophilic addition of the carboxyl group to the allene. (3-Chloro-3-butenoyl)pantetheine irreversibly inactivates the enzyme in a fashion similar to the acetylenic thio ester and also modifies a glutamate residue. Butyryl-CoA dehydrogenase catalyzes the isomerization of (3-butenoyl)pantetheine to (2-butenoyl)pantetheine. The enzyme catalyzes the elimination of HF from 3-fluoropropionyl-CoA and (3,3-difluorobutyryl)pantetheine. We suggest, that these results together support an oxidation mechanism for butyryl-CoA dehydrogenase which is initiated by alpha-proton abstraction.
mesh_terms: D000107:Acetylation; D044926:Butyryl-CoA Dehydrogenase; D055598:Chemical Phenomena; D002621:Chemistry; D004590:Electrophoresis, Paper; D044943:Fatty Acid Desaturases / Q000378:metabolism*; D005459:Fluorides / Q000378:metabolism; D010204:Pantetheine / Q000031:analogs & derivatives / Q000378:metabolism
chemical_list: C030179:3-butynoylpantetheine; D010204:Pantetheine; C030180:3-pentynoylpantetheine; D044943:Fatty Acid Desaturases; D044926:Butyryl-CoA Dehydrogenase; D005459:Fluorides