title: Two components of chorismate mutase in Brevibacterium flavum.
abstract: Chorismate mutase of Brevibacterium flavum, a common enzyme in phenylalanine and tyrosine biosynthesis, was separted into two different component, A and B, with molecular weights of 250,000 and 25,000, respectively, by ammonium sulfate fractionation or gel-filtration. Both components were essential for the enzymatic activity. In the presence of the reaction substrate, chorismate, the two components associated reversibly to give an active enzyme complex with a molecular weight of 320,000. Binding sites of the feedback inhibitors, phenylalanine and tyrosine, on the enzyme were localized on component A as determined by hybridization experiments with the wild-type and mutant components. Tyrosine repressed the synthesis of component B much more strongly than that of component A, while phenylalanine did not show any significant repressive effect on either component. The wild-type strain No. 2247 had four times more component A than component B. Elution patterns in gel, DEAE-cellulose or hydroxyapatite column chromatography as well as the disc-gel electrophoretic pattern of chorismate mutase component A and 3-deoxy-D-arabino-heptulosonate 7-phosphate (DAHP) synthetase activities completely overlapped, suggesting the presence of a bifunctional protein having the two activities. In accord with this suggestion, chorismate mutase as well as DAHP synthetase was insensitive to feedback inhibition by phenylalanine and tyrosine in all the 3-fluorophenylalanine-resistant mutants tested that excreted both phenylalanine and tyrosine. All the phenylalanine and tyrosine double auxotrophs defective in chorismate mutase lacked component B but not A.
mesh_terms: D001951:Brevibacterium / Q000201:enzymology*; D002826:Chorismate Mutase / Q000302:isolation & purification / Q000378:metabolism; D007535:Isomerases / Q000378:metabolism; D007700:Kinetics; D046911:Macromolecular Substances; D008970:Molecular Weight; D009154:Mutation; D010649:Phenylalanine / Q000494:pharmacology; D013045:Species Specificity; D014443:Tyrosine / Q000494:pharmacology
chemical_list: D046911:Macromolecular Substances; D014443:Tyrosine; D010649:Phenylalanine; D007535:Isomerases; D002826:Chorismate Mutase