Intramolecular electron transfer in the oxidation of amines by methylamine oxidase from Arthrobacter P1

Abstract

The intramolecular electron-transfer rate constant for the Cu(II)–topaNH2⇌ Cu(I)–topaSQ equilibrium in methylamine oxidase has been measured by temperature-jump relaxation techniques. At pH 7.0 the estimated kobs = 150±30 s–1 for both methylamine and benzylamine; assuming the equilibrium constant is ≈0.7–1 at pH 7.0 and 296 K, this would correspond to a forward electron-transfer rate constant kET≈ 60–75 s–1. Although substantially slower than the previously determined kET≈ 20 000 s–1 for pea seedling amine oxidase [5] steady-state kinetics measurements established that kET > kcat≈ 4–10 s–1. Thus the Cu(I)-semiquinone state is a viable intermediate in methylamine oxidase turnover.