Binding of harmane to human and bovine serum albumin: fluorescence and phosphorescence study

The binding of harmane with human serum albumin (HSA) and bovine serum albumin (BSA) were studied by fluorescence and phosphorescence spectroscopic methods. Quenching of fluorescence of serum albumins by harmane was found to be a static quenching process. The equilibrium constant (K) of complex formation was found to be equal to (5.16±0.28)x104 M-1 and (4.32±0.30)x104 M-1 for HSA and BSA, respectively. It was found that the interactions of harmane with HSA and BSA were also in the excited triplet state. The determined bimolecular constant or triplet state quenching (kqT)of the proteins studied by harmane was (1.15± 0.10)x107 M-1 s-1 and (2.88±0.22)x107 M-1 s-1 for HSA and BSA, respectively. Based on the similar value of K and kqT for HSA and BSA, a possible suggestion is that, most probably, the binding site of harmane is located in the drug site 1 in the subdomain IIa.