High valent iron oxo intermediates might be involved during activation of ribonucleotide reductase: single oxygen atom donors generate the tyrosyl radical.

The active form of protein B2, the small subunit of ribonucleotide reductase from E. Coli, contains a binuclear non heme iron center and a tyrosyl radical. MetB2 is an inactive form that lacks the radical but retains the Fe(III) center. We earlier proposed that the function of the iron center was to catalyze the one-electron oxidation of the tyrosine residue from metB2 by dioxygen. We now report that incubation of metB2 with single oxygen atom donors, hydrogen peroxide, 3-chloroperoxybenzoic acid, monoperoxophtalate and 2-iodosobenzoate, also results in the formation of the tyrosyl radical, as monitored by UV-visible and EPR spectroscopy. A mechanism of reductive activation of dioxygen by the binuclear non heme iron center involving iron-oxo intermediates is proposed.