Spin effects in reductive activation of O2 by oxydase enzymes

Reductive activation of O2 by glucose oxidase and by copper amine oxidases (and also by tyrosine hydroxylase and lypoxygenase) illustrate very interesting spin chemistry. The rate-determining step in these processes is connected with electron transfer from reduced cofactor (E) to O2 and is, in fact, the triplet –> singlet intersystem crossing (ISC) at the stage of the radical pair O2 − . . . E+ production. In glucose oxidase (and in similar enzymes without metal ions) the ISC is induced by spin-orbit coupling in O2 − ion. In copper amine oxidases, tyrosine hydroxylase and lypoxygenase the ISC is faster (104 times acceleration by presence of paramagnetic metal ion): it is induced by O2 −exchange interaction with metal. Exchange between metal spin and that of organic E+ cation is much weaker. This difference induces spin flip in the O2 − . . . E+ radical pair.