The mechanism of O2 reduction by copper amine oxidase from Arthrobacter globiformus (AGAO) is analyzed in relation to the cobalt-substituted protein. The enzyme utilizes a tyrosine-derived topaquinone cofactor to oxidize primary amines and reduce O2 to H 2O2. Steady-state kinetics indicate that amine-reduced CuAGAO is reoxidized by O2 >103 times faster than the CoAGAO analogue. Complementary spectroscopic studies reveal that the difference in the second order rate constant, kcat/KM(O2), arises from the more negative redox potential of CoIII/II in relation to CuII/I. Indistinguishable competitive oxygen-18 kinetic isotope effects are observed for the two enzymes and modeled computationally using a calibrated density functional theory method. The results are consistent with a mechanism where an end-on (η1)-metal bound superoxide is reduced to an η1-hydroperoxide in the rate-limiting step.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Surfaces, Coatings and Films
- Materials Chemistry