INTRAMOLECULAR ELECTRON-TRANSFER IN ASCORBATE OXIDASE IS ENHANCED IN THE PRESENCE OF OXYGEN

Intramolecular electron transfer from the type 1 copper center to the type 3 copper(II) pair is induced in the multi-copper enzyme, ascorbat e oxidase, following pulse radiolytic reduction of the type 1 Cu(II) i on. In the presence of a slight excess of dioxygen over ascorbate oxid ase, interaction between the trinuclear copper center and O-2 is obser ved even with singly reduced ascorbate oxidase molecules. Under these conditions, the rate constant for intramolecular electron transfer fro m type 1 Cu(I) to type 3 Cu(II) increases 5-fold to 1100 +/- 300 s(-1) (20 degrees C, pH 5.8) as compared to that of the same process under anaerobic conditions. This observation constitutes evidence for contro l of the internal electron transfer process by one of its substrates. The structural and functional significance of these findings are discu ssed.