Bullfrog thyroglobulin was digested with lysyl endopeptidase, known to be highly specific to cut the C‐terminal side of lysine residue in protein, after reduction and car☐ymethylation. We isolated one peptide which lacked the C‐terminal lysine, and which corresponds to 103–129 of bovine thyroglobulin sequence. Tyrosine 130 in the mammalian thyroglobulin molecule is known to be an iodination site. These findings suggest that tyrosine 130 in frog thyroglobulin is a thyroid hormone generating site.
