title: Stereoselectivity and stereospecificity of the alpha,beta-dihydroxyacid dehydratase from Salmonella typhimurium.
abstract: 1. In addition to the known 2R,3R- and 2R, 3S-2,3-dihydroxy-3-methylpentanoic acids (DHI), the 1S,3S- and sS,DR-isomers were prepared. 2S-2,3-Dihydroxy-3-methylbutanoic acid (DHV) was also prepared in addition to the known 2R-isomer. 2. The six dihydroxy acids were examined for their ability to promote the growth of isoleucine-valine (ilv)-requiring strains of Salmonella typhimurium and to serve as substrates for the alpha,beta-dihydroxyacid dehydratase of the same organism. 3. Only 2R,3R-2,3-dihydroxy-3-methylpentanoic and 2R-2,3-dihydroxy-3-methylbutanoic acids supported growth of the ilv strains of S. typhimurium. 4. alpha,beta-Dihydroxyacid dehydratase utilized the three isomers with the 2R-configuration as substrates but not those with the 2S-configuration. 5. In an additional growth study that utilized the 3R- and 3S-isomers of 3-methyl-2-oxopentanoic acid, the alpha-keto acid analogue of isoleucine, only the 3S-isomer supported growth. 6. It is concluded that the mechanism of action of the dehydratase is stereospecific in that the proton that is attached to C-3 of the substrate occupies the same steriochemical position as the departing hydroxyl group (Fig. 6).
mesh_terms: D002455:Cell Division; D002942:Circular Dichroism; D006836:Hydro-Lyases / Q000378:metabolism*; D006880:Hydroxy Acids / Q000138:chemical synthesis / Q000378:metabolism; D008968:Molecular Conformation; D009154:Mutation; D012486:Salmonella typhimurium / Q000201:enzymology* / Q000378:metabolism; D013045:Species Specificity; D013237:Stereoisomerism; D013329:Structure-Activity Relationship
chemical_list: D006880:Hydroxy Acids; D006836:Hydro-Lyases; C020052:dihydroxyacid dehydratase