rdf-syntax-grammar
mods:
  schema location: http://www.loc.gov/mods/v3 http://www.loc.gov/standards/mods/v3/mods-3-2.xsd
  title info:
    title: Mechanism of oxygen activation and hydroxylation by the aromatic amino acid hydroxylases
  name:
    name part: Pavon, Jorge A.
    role:
      role term: creator
  name:
    name part: Kunkel, Gary R.
    role:
      role term: thesis advisor.
  name:
    name part: Fitzpatrick, Paul F.
    role:
      role term: thesis advisor.
  type of resource: text
  genre: bibliography
  origin info:
    place:
      place term: txu
    date issued: 2010
    issuance: monographic
  language:
    language term: eng
  physical description:
    form: remote
    extent: 1 online resource.
  abstract: The aromatic amino acid hydroxylases phenylalanine hydroxylase (PheH), tyrosine hydroxylase (TyrH) and tryptophan hydroxylase (TrpH) utilize tetrahydropterin and molecular oxygen to catalyze aromatic hydroxylation. All three enzymes have similar active sites and contain an iron atom facially coordinated by two histidines and a glutamate. The three enzymes also catalyze the benzylic hydroxylation of 4- methylphenylalanine. The intrinsic primary and ?-secondary isotope effects for benzylic hydroxylation and their temperature dependences are nearly identical for the three enzymes, suggesting that the transition states, the tunneling contributions and the reactivities of the iron centers are the same. When molecular oxygen and the tetrahydropterin are replaced by hydrogen peroxide (H2O2), these enzymes catalyze the hydroxylation of phenylalanine to form tyrosine and meta-tyrosine with nearly identical second order rate constants. When the H2O2-dependent reaction is carried out with cyclohexylalanine or 4-methylphenylalanine, the products are 4-HO-cyclohexylalanine and 4-hydroxymethylphenylalanine, respectively. These experiments provide further evidence that the intrinsic reactivities of the iron centers in these enzymes are the same. Wild-type PheH and the uncoupled mutant protein V379D exhibit normal and inverse isotope effects, respectively, with deuterated phenylalanines. When the reaction is monitored by stopped-flow absorbance spectroscopy, three steps are visible. The first step is the reversible binding of O2, the second step is 5-7 fold faster than the turnover number, setting a limiting value for the rate constant for O2 activation, and the last step is non-enzymatic. There is no burst in the pre-steady state formation of tyrosine. These results are consistent with formation of the new C-O bond to form tyrosine as the ratelimiting step of the reaction. The reaction of TrpH with both tryptophan and phenylalanine was studied by stopped-flow absorbance spectrosco…
  note: by Jorge A. Pavon.
  note: "Major Subject: Biochemistry"
  note: Title from author supplied metadata (automated record created 2010-08-20 08:31:34).
  note: Electronic resource.
  note: Doctor of Philosophy Texas A&M University 2009 http://hdl.handle.net/1969.1/ETD-TAMU-2009-05-434
  note: Includes bibliographical references.
  note: Text (Dissertation)
  subject:
    topic: Major biochemistry
  subject:
    topic: isotope effects
  subject:
    topic: mechanistic enzymology
  subject:
    topic: transient kinetics
  subject:
    topic: metallo-enzymes
  identifier: http://hdl.handle.net/1969.1/ETD-TAMU-2009-05-434
  record info:
    record content source: TXA
    record creation date: 100907
    record change date: 20151201155028.0
    record identifier: in00002601665