Spectrophotofluorimetric study of the interaction between Trazodone hydrochloride and bovine serum albumin

The binding of trazodone hydrochloride (TZH), an antidepressant drug, to bovine serum albumin (BSA) has been investigated by fluorescence spectroscopic analysis. The fluorescence emission of BSA (lambda(em) = 350 nm) was quenched by TZH while that of this ligand was enhanced (lambda(em) = 443 nm). The spectral behavior was consistent with the static quenching mechanism, and the apparent binding constant, K-a (1.05 x 10(4) l mol(-1)) as well as binding site number, n (similar to 1), were estimated. Thermodynamic parameters obtained from the measured data at different temperatures showed that the binding of TZH to BSA involved predominantly hydrophobic interactions as well as smaller contributions from electrostatic forces. Phenylbutazone and ibuprofen were utilized as competitive markers for sites I and II, respectively, in the interaction of TZH with BSA. This competitive displacement procedure indicated that the likely binding was site I, i.e., subdomain IIA, and this was supported by the observation that up to 50% of this site marker, phenylbutazone, could be exchanged with TZH whilst only a few percent of ibuprofen were so affected.