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 oxida se has been measured by temperature-jump relaxation techniques. At pH 7.0 the estimated k(obs) = 150+/-30 s(-1) for both methylamine and ben zylamine; assuming the equilibrium constant is approximate to 0.7-1 at pH 7.0 and 296 K, this would correspond to a forward electron-transfe r rate constant k(ET) approximate to 60-75 s(-1). Although substantial ly slower than the previously determined k(ET) approximate to 20000 s( -1) for pea seedling amine oxidase [5] steady-state kinetics measureme nts established that k(ET) > k(cat) approximate to 4-10 s(-1). Thus th e Cu(I)-semiquinone state is a viable intermediate in methylamine oxid ase turnover.