[Differences in the secondary structure of thyroglobulin under normal conditions and in nodular goiter].

Intact and iodine-treated thyroglobulin from normal thyroid gland and from nodular euthyroid goiter were studied by means of circular dichroism to detect differences in the protein secondary structure. Contents of alpha- and beta-structures in thyroglobulins were differentiated only by several per cents but artificial iodination of the protein increased markedly the difference between thyroglobulins of various origin. Extrapolation of the data to "zero" content of iodine-containing amino acids demonstrated that the initial steps of thyroglobulin synthesis occurring before iodination "in vitro", appears to be also responsible for alterations in the protein secondary structure.