L-thyroxine 595.61279296875 595.67999267578125 758.6761474609375 758.8499755859375 O-(4-hydroxy-3,5-diiodophenyl)-3,5-diiodo-L-tyrosine C 6 O 1 I 4 MOD_RES Thyroxine A protein modification that effectively substitutes an L-tyrosine residue with L-thyroxine. Y none I4Thy 3,3',5,5'-tetraiodo-L-thyronine 3',3'',5',5''-tetraiodo-L-thyronine PSI-MOD tetraiodo 4-(4-hydroxy-3,5-diiodophenoxy)-3,5-diiodo-L-phenylalanine T4 L-thyroxine MOD:00187 3,5,3',5'-tetraiodo-L-thyronine natural Thyroxine (S)-2-amino-3-[4-(4-hydroxy-3,5-diiodophenoxy)-3,5-diiodophenyl]propanoic acid C 15 H 9 N 1 O 3 I 4 iodinated tyrosine