title: Inhibition of tyrosine phenol-lyase by tyrosine homologues.
abstract: We have designed, synthesized, and evaluated tyrosine homologues and their O-methyl derivatives as potential inhibitors for tyrosine phenol lyase (TPL, E.C. 4.1.99.2). Recently, we reported that homologues of tryptophan are potent inhibitors of tryptophan indole-lyase (tryptophanase, TIL, E.C. 4.1.99.1), with K i values in the low µM range (Do et al. Arch Biochem Biophys 560:20-26, 2014). As the structure and mechanism for TPL is very similar to that of TIL, we postulated that tyrosine homologues could also be potent inhibitors of TPL. However, we have found that homotyrosine, bishomotyrosine, and their corresponding O-methyl derivatives are competitive inhibitors of TPL, which exhibit K i values in the range of 0.8-1.5 mM. Thus, these compounds are not potent inhibitors, but instead bind with affinities similar to common amino acids, such as phenylalanine or methionine. Pre-steady-state kinetic data were very similar for all compounds tested and demonstrated the formation of an equilibrating mixture of aldimine and quinonoid intermediates upon binding. Interestingly, we also observed a blue-shift for the absorbance peak of external aldimine complexes of all tyrosine homologues, suggesting possible strain at the active site due to accommodating the elongated side chains.
authors.affiliation: Department of Chemistry, University of Georgia, Athens, GA, 30602, USA.|Hill Manufacturing Co., Inc., 1500 Jonesboro Rd SE, Atlanta, GA, 30315, USA.
authors.forename: Quang
authors.initials: Q
authors.lastname: Do
authors.affiliation: Department of Chemistry, University of Georgia, Athens, GA, 30602, USA.|, Adelaide, Australia.
authors.forename: Giang T
authors.initials: GT
authors.lastname: Nguyen
authors.affiliation: Department of Chemistry, University of Georgia, Athens, GA, 30602, USA. plp@uga.edu.|Department of Biochemistry and Molecular Biology, University of Georgia, Athens, GA, 30602, USA. plp@uga.edu.
authors.forename: Robert S
authors.initials: RS
authors.lastname: Phillips
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics; D016971:Citrobacter freundii / Q000201:enzymology* / Q000235:genetics; D004791:Enzyme Inhibitors / Q000737:chemistry*; D014443:Tyrosine / Q000031:analogs & derivatives / Q000737:chemistry; D014447:Tyrosine Phenol-Lyase / Q000737:chemistry* / Q000235:genetics
chemical_list: D001426:Bacterial Proteins; D004791:Enzyme Inhibitors; D014443:Tyrosine; D014447:Tyrosine Phenol-Lyase
keywords: Amino acid homologue; Pyridoxal-5′-phosphate; Reaction mechanism; Stopped-flow kinetics; β-Elimination