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Tryptophan 409 controls the activity of neuronal nitric-oxide synthase by regulating nitric oxide feedback inhibition

Academic Article
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Overview

authors

  • Adak, S.
  • Crooks, C.
  • Wang, Q.
  • Crane, Brian R
  • Tainer, John
  • Getzoff, Elizabeth
  • Stuehr, D. J.

publication date

  • 1999

journal

  • Journal of Biological Chemistry  Journal

abstract

  • The heme of neuronal nitric-oxide synthase participates in oxygen activation but also binds self-generated NO during catalysis resulting in reversible feedback inhibition. We utilized point mutagenesis to investigate if a conserved tryptophan residue (Trp-409), which engages in pi-stacking with the heme and hydrogen bonds to its axial cysteine ligand, helps control catalysis and regulation by NO. Surprisingly, mutants W409F and W409Y were hyperactive compared with the wild type regarding NO synthesis without affecting cytochrome c reduction, reductase-independent N-hydroxyarginine oxidation, or Arg and tetrahydrobiopterin binding. In the absence of Arg, NADPH oxidation measurements showed that electron flux through the heme was actually slower in the Trp-409 mutants than in wild-type nNOS. However, little or no NO complex accumulated during NO synthesis by the mutants, as opposed to the wild type. This difference was potentially related to mutants forming unstable 6-coordinate ferrous-NO complexes under anaerobic conditions even in the presence of Arg and tetrahydrobiopterin. Thus, Trp-409 mutations minimize NO feedback inhibition by preventing buildup of an inactive ferrous-NO complex during the steady state. This overcomes the negative effect of the mutation on electron flux and results in hyperactivity. Conservation of Trp-409 among different NOS suggests that the ability of this residue to regulate heme reduction and NO complex formation is important for enzyme physiologic function.

subject areas

  • Escherichia coli
  • Feedback
  • Hydrogen Peroxide
  • Kinetics
  • Models, Chemical
  • Models, Molecular
  • NADP
  • Nitric Oxide
  • Nitric Oxide Synthase
  • Nitric Oxide Synthase Type I
  • Point Mutation
  • Structure-Activity Relationship
  • Tryptophan
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Identity

International Standard Serial Number (ISSN)

  • 0021-9258

Digital Object Identifier (DOI)

  • 10.1074/jbc.274.38.26907

PubMed ID

  • 10480900
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Additional Document Info

start page

  • 26907

end page

  • 26911

volume

  • 274

issue

  • 38

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