Abstract
The binding of thyroxine (T4) to bovine serum albumin (BSA) has been studied in the presence and absence of Ca2+, Cu2+ and Zn2+ ions at various pH's in 0.1 M Tris-acetate buffer at 25 degrees C using the fluorescence method. In the presence of 50 microM Ca2+ and Zn2+ and the absence of metal ions, the binding constant (K) increased similarly with increasing pH values from pH 5 to pH 9, and the K value near midpoint, pH 7.4, was 1.66 +/- 0.17 x 10(6) M-1. By contrast, the binding constant remained constant between pH5 and pH9 in the presence of 10 microM Cu2+, with an average value of 1.61 +/- 0.22 x 10(6) M-1, suggesting a significant influence of Cu2+ ions on T4 binding to BSA.

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