title: A single cyclohexadienyl dehydratase specifies the prephenate dehydratase and arogenate dehydratase components of one of two independent pathways to L-phenylalanine in Erwinia herbicola.
abstract: Dual biosynthetic pathways diverge from prephenate to L-phenylalanine in Erwinia herbicola, the unique intermediates of these pathways being phenylpyruvate and L-arogenate. After separation from the bifunctional P-protein (one component of which has prephenate dehydratase activity), the remaining prephenate dehydratase activity could not be separated from arogenate dehydratase activity throughout fractionation steps yielding a purification of more than 1200-fold. The ratio of activities was constant after removal of the P-protein, and the two dehydratase activities were stable during purification. Hence, the enzyme is a cyclohexadienyl dehydratase. The native enzyme has a molecular mass of 73 kDa and is a tetramer made up of identical 18-kDa subunits. Km values of 0.17 mM and 0.09 mM were calculated for prephenate and L-arogenate, respectively. L-Arogenate inhibited prephenate dehydratase competitively with respect to prephenate, whereas prephenate inhibited arogenate dehydratase competitively with respect to L-arogenate. Thus, the enzyme has a common catalytic site for utilization of prephenate or L-arogenate as alternative substrates. This is the first characterization of a purified monofunctional cyclohexadienyl dehydratase.
authors.affiliation: Department of Microbiology and Cell Science, University of Florida, Gainesville 32611.
authors.forename: T H
authors.initials: TH
authors.lastname: Xia
authors.forename: S
authors.initials: S
authors.lastname: Ahmad
authors.forename: G S
authors.initials: GS
authors.lastname: Zhao
authors.forename: R A
authors.initials: RA
authors.lastname: Jensen
mesh_terms: D002848:Chromatography, DEAE-Cellulose; D002850:Chromatography, Gel; D002852:Chromatography, Ion Exchange; D004885:Erwinia / Q000201:enzymology*; D006836:Hydro-Lyases / Q000302:isolation & purification* / Q000378:metabolism; D007700:Kinetics; D008970:Molecular Weight; D009097:Multienzyme Complexes / Q000302:isolation & purification* / Q000378:metabolism; D010649:Phenylalanine / Q000096:biosynthesis*; D011302:Prephenate Dehydratase / Q000302:isolation & purification* / Q000378:metabolism
chemical_list: D009097:Multienzyme Complexes; D010649:Phenylalanine; D006836:Hydro-Lyases; C022437:pretyrosine dehydratase; D011302:Prephenate Dehydratase