JBC, Vol. 250, Issue 16, 6417-6423, Aug, 1975
Binding of selected iodothyronine analogues to receptor sites of isolated rat hepatic nuclei. High correlation between structural requirements for nuclear binding and biological activity
D. Koerner, H. L. Schwartz, M. I. Surks and J. H. Oppenheimer
The limited capacity, high affinity binding of 35 iodothyronine analogues
by rat liver nuclei has been examined in an in vitro system. The in vitro
nuclear binding of all the analogues tested was highly correlated with
their published thyromimetic potencies in the intact animals. Binding and
biological activity are greater for 3'-mono-than 3',5'-di-substituted
iodothyronines. A 4'-hydroxyl group is essential, but the 3' substituent
can be several halogen or non-halogen groups for which the distal
conformation is preferred. The ether linkage can be replaced equally well
by a methylene or sulfur group. The presence of both 3 and 5 groups which
are limited to halogens or small alkyl groups are necessary for the
maintenance of significant activity. Halogen-free iodothyronines have very
low, but significant activity both in vitro and in vivo. The data provide
information on the structural requirements for thyroid hormone action and
further support the physiological relevance of the nuclear sites.