Polypeptide Chains of 19‐S Thyroglobulin from Several Mammalian Species and of Porcine 27‐S Iodoprotein

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Abstract
Undegraded 19-S thyroglobulin [TG] was purified from hog, ox, man, dog, sheep and rat thyroid glands. Sodium dodecylsulfate/polyacrylamide gel electrophoresis of the reduced proteins showed that all are formed of peptide chains of MW about 330,000. Carboxypeptidase A digestion of porcine 19-S TG released consecutively 2 mol leucine and then 2 mol serine, offering strong evidence in favor of the idea that the protein is formed of 2 identical chains. The same C-terminal amino acids were detected in sheep, ox, dog and man TG. No N-terminal amino acid was found by appropriate chemical and enzymatic techniques. Porcine 27-S iodoprotein was shown by carboxypeptidase A analysis to be formed of 4 single-stranded 330,000-Mr [molecular weight] subunits identical to those constituting the 19-S protein. Identity, both qualitatively and quantitatively, of the peptides obtained by CNBr cleavage of the 2 proteins as shown by sodium dodecylsulfate/polyacrylamide gel electrophoresis confirmed this conclusion. Since 19-S and 27-S thyroid iodoproteins are formed of 2 and 4 probably chains, they must be termed 19-S and 27-S TG or alternatively TG dimer and tetramer, respectively.

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