Thyroxine-induced conformational changes in prealbumin

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Abstract
The effects of thyroxine [T4] binding on the conformation of human prealbumin and bovine serum albumin were examined. A blue shift in protein absorption was observed with prealbumin, whereas a red shift was observed with bovine serum albumin. In the case of prealbumin, where the 2 binding sites are identical, the total absorption change was confined to the binding of the 1st ligand and was interpreted as resulting from a conformational change. A blue shift observed in the absorption spectrum of T4 was the same for the 1st and 2nd bound molecules. These data were interpreted in terms of 2 identical and interacting sites on prealbumin and explain the origin of the difference in binding affinities between the 1st and 2nd sites. Fluorescence quenching by T4 and T4 effects on tryptic hydrolysis of prealbumin are in accord with the above interpretation.