Spectroscopic Studies on the Mode of Interaction of an Anticancer Drug with Bovine Serum Albumin

The mechanism of interaction of vinblastin sulphate (VBS) with bovine serum albumin (BSA) has been reported. Association constant for VBS-BSA binding was found to be 3.146+/-0.06 x 10(4) M(-1). Stern-Volmer analysis of fluorescence quenching data showed that the fraction of fluorophore (protein) accessible to the quencher (drug) was close to unity indicating thereby that both tryptophan residues of BSA are involved in drug-protein interaction. The rate constant for quenching, greater than 10(10) M(-1) S(-1), indicated that the drug-binding site is in close proximity to tryptophan residues of BSA. Binding studies in the presence of an hydrophobic probe, 8-anilino-1-naphthalein-sulphonic acid, sodium salt (ANS) indicated that there is hydrophobic interaction between VBS and probe and they do not share common sites in BSA. Thermodynamic parameters obtained from data at different temperatures showed that the binding of VBS to BSA involves predominant hydrophobic forces. The effects of some additives and paracetamol on binding of VBS-BSA have also been investigated. The CD spectrum of BSA in presence of VBS shows that the binding of VBS leads to change in the helicity of BSA.