Reports

Thyroxine-Binding Globulin: Characterization of the Binding Site with a Fluorescent Dye as a Probe

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Science  24 Mar 1972:
Vol. 175, Issue 4028, pp. 1378-1380
DOI: 10.1126/science.175.4028.1378

Abstract

The fluorescent dye 1,8-anilinonaphthalenesulfonate competed with thyroxine for binding to thyroxine-binding globulin. Fluorescence analysis indicated that the dye bound to the globulin in a molar ratio of 1:1 and with an association constant (at 23°C) of 4.19 x106M-1, and that thyroxine bound to the globulin in a molar ratio of 1:1 and with an association constant (at 23°C) of 2.35x1010M-1. Displacement of globulin-bound dye by thyroxine was shown by fluorescence quenching, and displacement of globulin-bound thyroxine by dye was demonstrated by ultrafiltration.

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