In vitro triiodothyronine binding to non-histone proteins from rat liver nuclei

Abstract

In vitro incubations of non-histone proteins from rat liver nuclei with labelled L-3, 5, 3′ triiodothyronine demonstrate the existence of high affinity, limited capacity binding sites for the hormone in this protein group; the affinity was found identical for triiodothyroacetic acid and lower for L-thyroxine. Binding ability was highly temperature dependent. At 4°C, the rate constant of association was 0.9 × 10 7 M −1 h −1 and the rate constant of dissociation was 0.015 h −1. The dissociation constant K d was calculated from these data or measured by Scatchard analysis and found to be between 1.6 and 5 × 10 −9 M. The maximum binding capacity was 10 −13 moles of L-3, 5, 3′ triiodothyronine per 100 μg non-histone proteins or 6000 hormone molecules per nucleus. Protein binding had a half-life of 20 hours at 4°C, in the absence of hormone, but was found to be very stable in the presence of hormone.