26 In vitro: 2I - + 2H + + 2H 2 O I 2 + 2H 2 O Iodination of tyrosine. Iodine is oxidized by thyroid peroxidase in a 2e - oxidation step, forming I +. The phenolate anion of tyrosine is in equilibrium with its quinoid form. Iodinium and tyrosine quinoid react to form an iodinated quinoid intermediate that forms MIT by electronic rearrangement. (b) Iodine is oxidized by thyroid peroxidase in a 1e - step forming a free radical (I 0 ). The quinoid anion of tyrosine is oxidized to a free radical by peroxidase or by another I0. The quinoid free radical reacts with I 0 to form MIT by electronic rearrangement.