Human serum albumin and quercetin interactions monitored by time-resolved fluorescence: evidence for enhanced discrete rotamer conformations.

Human serum albumin (HSA) complexation with quercetin, a flavonoid commonly present in human diet, was monitored by means of fluorescence decays of the single HSA tryptophan - Trp214. Data analysis based on fitting to multiexponential functions and determining the lifetime distributions revealed a high sensitivity of tryptophan fluorescence to binding quercetin. Results are discussed in terms of the rotamer model for tryptophan, HSA-quercetin complexation and potential HSA to quercetin energy transfer. Evidence for quercetin stabilising tryptophan rotamers in HSA is presented.