Spectroscopic Study of the Interaction Between Folic Acid and Bovine Serum Albumin

The interaction between folic acid and bovine serum albumin (BSA) was investigated by spectroscopic methods including fluorescence, circular dichroism (CD), and UV‐Vis absorption adsorption spectroscopies. The binding constant K A and the number of binding sites, n, were determined based on the fluorescence quenching of BSA in the presence of folic acid. The thermodynamic parameters ΔH, ΔG, ΔS at different temperatures were calculated, and the results indicated that the acting force between folic acid and BSA was mainly hydrogen bonding. The distance between the donor (BSA) and acceptor (folic acid) was obtained according to Förster's theory of nonradiational energy transfer. The quenching mechanism of the BSA–folic acid system is a combination of static quenching and nonradiative energy transfer. The CD and synchronous fluorescence spectra were used to investigate the structural change of BSA upon addition of folic acid, and the result indicated that the secondary structure of BSA changed in the presence of folic acid.