The Binding of Thyroid Hormones to Bovine Serum Albumin as Measured by Circular Dichroism

The circular dichroism (CD) spectra of 3,5,3'-triiodothyronine-bovine serum albumin (T3-BSA) and thyroxine-bovine serum albumin (T4-BSA) complexes were measured at the various ratios of T3 or T4 to BSA (T/P) in the wavelength region of 200-350 nm. No spectral change was observed in the chromophoric wavelength region of 250-350 nm. The value of [omicron] at 319 nm of the induced Cotton effect increased with increase of the T/P ratio in both complexes, and in T4-BSA complex, it increased remarkably. The number of thyroid hormone molecules bound to one BSA molecule was estimated to be one in the case of T4-BSA complex and four to five in T3-BSA.