Studies of Thyroid Hormones (Propylthiouracil and L-Thyroxine) Interaction with Human Serum Albumin-Spectroscopic Approach

Abstract

In this work, UV-absorption, fluorescence spectroscopy and Fourier transform infrared (FTIR) spectroscopy were used to investigate the relationship between Propylthiouracil and L-Thyroxine with human serum albumin. The binding constants of propylthiouracil and L-Thyroxine have been determined of both UV-absorption and fluorescence spectroscopy. The binding Constants values measured at 293k are 1.659×10³ M^-1 for propylthiouracil and 1.013×10⁴ M^-1 for L-Thyroxine. The constant values of the Stern–Volmer quenching were determined to be 2.144×10³ L mol^-1 for propylthiouracil and 1.937×10³ L mol^-1 L-for Thyroxine. The UV-absorption intensity of HSA- hormones complexes has increased with increasing of propylthiouracil and L-Thyroxine concentration. With the rise in propylthiouracil and L-thyroxine concentrations, the fluorescence results indicate a decrease in HSA- hormone emission intensity. To determine the effects of protein secondary structure and hormone binding mechanisms, we have used FTIR spectroscopy with Fourier self-deconvolution technique and second derivative resolution enhancement, as well as curve-fitting methods for the investigation of the amide I, II, and III regions. The peak positions within the three amide regions (amide I, amide II and amide III) were allocated and any results were explored due to changes in concentration. Due to variations in hormone concentrations, the measurements of the FTIR spectra indicate a difference in the intensity of absorption bands.. FTIR Spectra measurements reflect a difference in the strength of the absorption bands due to changes in hormone concentrations.