Temperature effect on the structural stability, similarity, and reversibility of human serum albumin in different states

In order to investigate the thermal stability of human serum albumin (HAS) in three different states (aqueous solution, cast film, and solid powder), Fourier transform infrared (FTIR) spectroscopy was applied to determine the protein secondary structural changes of these HSA samples under non-isothermal or isothermal condition. The structural similarity of HSA before and after thermal treatment was also studied to estimate the thermo-reversible property of the HSA in these different states. The results indicate that with the increase of temperature, the maximum peaks at 1652 and 1547 cm−1 (α-helix) shifted to 1647 and 1542 cm−1 (random coil), respectively. An additional peak at 1620 cm−1 assigned to intermolecular β-sheet structure clearly appeared with temperature. The α-helix content was found to be reduced in favor of the formation of intermolecular hydrogen-bonded antiparallel β-sheet structure beyond 60 °C in the heating process. From the data of structural similarity, HSA sample whether in solid powder or cast film form exhibited a better thermo-reversible property than HSA in aqueous solution even heating to 200 °C.