Polypeptide chains of 19-S thyroglobulin from several mammalian species and of porcine 27-S iodoprotein

Abstract

Undegraded 19-S thyroglobulin 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 molecular weight about 330000. Carboxypeptidase A digestion of porcine 19-S thyroglobulin released consecutively two moles of leucine and then two moles of serine, thus offering strong evidence in favour of the idea that the protein is formed of two identical chains. The same C-terminal amino acids were detected in sheep, ox, dog and man thyroglobulins. 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 four single-stranded 330000-Mr subunits identical to those constituting the 19-S protein. Identity, both qualitatively and quantitatively, of the peptides obtained by CNBr cleavage of the two proteins as shown by sodium dodecylsulfate/polyacrylamide gel electrophoresis has confirmed this conclusion. Since 19-S and 27-S thyroid iodoproteins are formed of two and four probably identical chains, they must be termed 19-S and 27-S thyroglobulins or alternatively thyroglobulin dimer and tetramer, respectively.