Analysis of Binding Interaction between Captopril and Human Serum Albumin

The interaction between captopril, an inhibitor of angiotensin converting enzyme and human serum albumin, a principal plasma protein in the liver has been investigated in vitro under a simulated physiological condition by UV-vis spectrophotometry and fluorescence spectrometry. The intrinsic fluorescence intensity of human serum albumin was strongly quenched by captopril. The binding constants and the number of binding sites can be calculated from the data obtained from fluorescence quenching experiments. The negative value of ΔG0 reveals that the binding process is a spontaneous process. According to the van’t Hoff equation, the standard enthalpy change (ΔH0) and standard entropy change (ΔS0) for the reaction were calculated to be 35.98 KJ●mol-1 and 221.25 J●mol-1 K. It indicated that the hydrophobic interactions play a main role in the binding of captopril to human serum albumin. In addition, the distance between captopril (acceptor) and tryptophan residues of human serum albumin (donor) was estimated to be 1.05 nm according to the Forster’s resonance energy transfer theory. The results obtained herein will be of biological significance in pharmacology and clinical medicine.