Steady state and time-resolved fluorescence investigation of the specific binding of two chlorin derivatives with human serum albumin

The specific binding of two model drugs for photodynamic therapy, namely chlorin P-6 and purpurin 18 in the vicinity of Sudlow's Site I of HSA has been investigated by monitoring the intrinsic fluorescence of single tryptophanyl residue and by competitive binding with warfarin. The distance from the tryptophanyl residue has been ascertained by FRET from Trp to the chlorins and has been found to indicate a binding to Sudlow's Site i. The principal driving force for the interaction is found to be the hydrophobic effect. The main mechanism of protein fluorescence quenching was static. Time-resolved fluorescence results of competitive binding with warfarin are found to confirm that they bind to the warfarin binding site.