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

 The intramolecular electron-transfer rate constant for the Cu(II)–topa_NH2⇌ Cu(I)–topa_SQ equilibrium in methylamine oxidase has been measured by temperature-jump relaxation techniques. At pH 7.0 the estimated k_obs = 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 k_ET≈ 60–75 s^–1. Although substantially slower than the previously determined k_ET≈ 20 000 s^–1 for pea seedling amine oxidase 5] steady-state kinetics measurements established that k_ET > k_cat≈ 4–10 s^–1. Thus the Cu(I)-semiquinone state is a viable intermediate in methylamine oxidase turnover. Received: 16 August 1995 / Accepted: 21 December 1995