Thyroglobulin biosynthesis: An ultracentrifugal study

This work presents data on the biosynthesis of thyroglobulin. This protein of 19S size constitutes the main thyroid protein in most normal vertebrate thyroid glands; smaller amounts of 3-8S and 27S protein are usually present. Initially it is shown that in vivo in the rat, as has been previously shown in vitro by other workers, labelled amino acids are incorporated into proteins of 3-8S and 12S size before the label is incorporated into thyroglobulin. The pattern of incorporation is consistent with the 12S and with less certainty the 3-8S proteins being precursor subunits of the 19S protein. At long time intervals after administration of a pulse of 3H-leucine, the pattern of labelling of the 3-8S fraction could also be consistent with this labelled fraction being a breakdown product of the labelled 19S protein. These findings with 3H-leucine are in contrast to those seen when [125]I is used. In this case [125]I is not incorporated into proteins 19S. This occurred despite differences in distribution of the thyroid proteins in thyroid glands treated pre-operatively with these two different regimes. (Abstract shortened by ProQuest.)