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) reversible arrow 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 approximate to 0.7-1 at pH 7.0 and 296 K, this would correspond to a forward electron-transfer rate constant k(ET) approximate to 60-75 s(-1). Although substantially slower than the previously determined k(ET) approximate to 20000 s(-1) for pea seedling amine oxidase [5] steady-state kinetics measurements established that k(ET) > k(cat) approximate to 4-10 s(-1). Thus the Cu(I)-semiquinone state is a viable intermediate in methylamine oxidase turnover.