Jun 25, 1976

Thyroxine-protein interactions. Interaction of thyroxine and triiodothyronine with human thyroxine-binding globulin

The Journal of Biological Chemistry
L Korcek, M Tabachnick


The effect of temperature on the binding of thyroxine and triiodothyronine to thyroxine-binding globulin has been studied by equilibrium dialysis. Inclusion of ovalbumin in the dialysis mixture stabilized thyroxine-binding globulin against losses in binding activity which had been found to occur during equilibrium dialysis. Ovalbumin by itself bound the thyroid hormones very weakly and its binding could be neglected when analyzing the experimental results. At pH 7.4 and 37 degrees in 0.06 M potassium phosphate/0.7 mM EDTA buffer, thyroxine was bound to thyroxine-binding globulin at a single binding site with apparent association constants: at 5 degrees, K = 4.73 +/- 0.38 X 10(10) M-1; at 25 degrees, K = 1.55 +/- 0.17 X 10(10) M-1; and at 37 degrees, K = 9.08 +/- 0.62 X 10(9) M-1. Scatchard plots of the binding data for triiodothyronine indicated that the binding of this compound to thyroxine-binding globulin was more complex than that found for thyroxine. The data for triiodothyronine binding could be fitted by asuming the existence of two different classes of binding sites. At 5 degrees and pH 7.4 nonlinear regression analysis of the data yielded the values n1 = 1.04 +/- 0.10, K1 = 3.35 +/- 0.63 X 10(9) M-1 and n2 = 1.40 +/- 0...Continue Reading

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Mentioned in this Paper

Thyroxine-Binding Globulin
Thyroxine Measurement
Hydatidiform Mole
Plasma Protein Binding Capacity
Ligand Binding Domain

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