Competitive binding of phenylbutazone and colchicine to serum albumin in multidrug therapy: A spectroscopic study

The binding sites for phenylbutazone and colchicine were identified in tertiary structure of bovine and human serum albumin with the use of spectrofluorescence analysis. It was found that phenylbutazone has two binding sites in both sera albumins (HSA and BSA), while colchicine has one binding site in BSA as well as in HSA. The comparison of the quenching effect of BSA and HSA fluorescence by phenylbutazone and colchicine allows us to identify subdomain IIA in protein as the binding site for these two drugs. In this subdomain tryptophan 214 is located. The participation of tyrosyl and tryptophanyl residues of protein was also estimated in the drug–albumin complex. The comparison of quenching of fluorescence of HSA and BSA excited at 280 nm with that at 295 nm allowed us to state that the participation of tyrosyl residues of albumin in the phenylbutazone–serum albumin interaction is significant.The analysis of quenching of fluorescence of BSA in the binary and ternary systems showed that phenylbutazone does not affect the complex formed between colchicine and BSA. Similarly, colchicine has no effect on the Phe–BSA complex. However marked differences were observed for the complex with HSA. On the basis of Ka and KQ values it was concluded that colchicine may probably cause displacement of phenylbutazone from its complex with serum albumin (SA). Static and dynamic quenching for the binary and ternary systems is also discussed.The competition of phenylbutazone and colchicine in binding to serum albumin should be taken into account in the multi-drug therapy.