Interaction of human serum albumin with sulfadiazine

In this report we have studied the interaction of sulfadiazine (SD), which has recently been found to partially protect the amyloidosis, with human serum albumin (HSA) at physiological conditions of temperature and pH. We have employed several basic and advanced spectroscopic techniques such as UV, fluorescence, circular dichroism (CD) and Fourier transform infra-red (FTIR) spectroscopies. UV spectrum of native HSA was different from the spectrum of HSA in the presence of SD due to the complex formation between albumin and drug. Fluorescence quenching of HSA by SD at 280 nm was due to the formation of HSA-SD complex. The data were analyzed using Stern-Volmer (SV) and the quenching was found to be static with 1:1 binding ratio. Synchronous fluorescence spectra have shown a red shift and revealed that hydrophobicity around both Trp and Tyr residues was decreased. CD results have shown that the conformation of macromolecule remains undisturbed at low concentrations (up to 20 mu M of the SD), though, a small change in the secondary structure from 20 to 75 mu M of SD was observed followed by a large change and consequent unfolding on further increase in the drug concentration. Both synchronous and CD measurements were consistent to each other. From the FTIR measurement analysis it was found that amide I band also shifted which concluded that the conformational changes take place in the presence of SD. (C) 2014 Elsevier B.V. All rights reserved.