Insights into the mechanism of flavoprotein-catalyzed amine oxidation from nitrogen isotope effects on the reaction of N-methyltryptophan oxidase

Biochemistry. 2007 Jun 26;46(25):7655-64. doi: 10.1021/bi700482h. Epub 2007 Jun 2.


The mechanism of N-methyltryptophan oxidase, a flavin-dependent amine oxidase from Escherichia coli, was studied using a combination of kinetic isotope effects and theoretical calculations. The 15(kcat/Km) kinetic isotope effect for sarcosine oxidation is pH-dependent with a limiting value of 0.994-0.995 at high pH. Density functional theory calculations on model systems were used to interpret these isotope effects. The isotope effects are inconsistent with proposed mechanisms involving covalent amine-flavin adducts but cannot by themselves conclusively distinguish between some discrete electron-transfer mechanisms and a direct hydride-transfer mechanism, although the latter mechanism is more consistent with the energetics of the reaction.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Amines / chemistry*
  • Catalysis
  • Escherichia coli / enzymology
  • Flavin-Adenine Dinucleotide / chemistry
  • Kinetics
  • Nitrogen Isotopes
  • Oxidation-Reduction
  • Oxidoreductases, N-Demethylating / chemistry
  • Oxidoreductases, N-Demethylating / genetics
  • Oxidoreductases, N-Demethylating / metabolism*


  • Amines
  • Nitrogen Isotopes
  • Flavin-Adenine Dinucleotide
  • Oxidoreductases, N-Demethylating