[thyroglobulin]-3-iodo-L-tyrosine + iodide + H2O2 + H(+) = [thyroglobulin]-3,5-diiodo-L-tyrosine + 2 H2O
[thyroglobulin]-3-iodo-l-tyrosine + iodide + h2o2 + h(+) = [thyroglobulin]-3,5-diiodo-l-tyrosine + 2 h2o