Abstract
Comparative evaluation of the incorporation of labelled amino acid into different
protein fractions of thyroid glands from normal rats was studied after in vivo injection
of the isotope (3H-tyrosine).
The maximum of incorporation into total thyroidal proteins was observed 30 min after
injection of the label and was maintained with small fluctuations during 5 hr. The
maximum of incorporation of the label into total thyroglobulin was obtained later
at 2 hr after injection. For the particulate thyroglobulin the maximum was observed
earlier than for soluble thyroglobulin.
Total thyroglobulin (soluble + particulate) represent 45-50% of newly formed thyroidal
proteins. The major part of thyroglobulin was found in the soluble protein fraction
from the shortest time after injection (30 min). A relative accumulation of thyroglobulin
in this fraction (% of the total thyroglobulin) was observed during the first 24 hr
following injection (70% at 30 min and 90% at 24 hr).
Among proteins other than thyroglobulin 35-40% were found in the fraction of soluble
proteins, while 60-65% were particulate in origin. By digitonin extraction 20-25%
of the latter proteins can be solubilized.
About 35% of newly formed proteins were degraded during the first 24 hours following
injection. Total thyroglobulin and the totality of proteins other than thyroglobulin
were degraded to the same proportions. It seems that thyroglobulin can be degraded
before being completely halogenated.
Key words
Thyroglobulin Synthesis - Protein Synthesis - Amino Acid Uptake - Thyroid Gland
