Interactions of protoporphyrin IX and its derivatives with benzodiazepine receptor

The aim of this study was to determine binding affinities of the Peripheral benzodiazepine receptor (PBR) with protoporphyrin IX, haematoporphyrin (Hp), and two arginized derivatives: Hp(Arg)2 and PP(Arg)2. The quenching of protein fluorescence was used to measure association constants during titration of PBR solution with PP derivatives in a function of concentration. The experimental data was fitted to theoretical curves, assuming strong and weak binding model with one binding site. As a result of this early study affinity constants were determined. The highest affinity toward PBR showed PPIX and Hp, Hp(Arg)2, PP(Arg)2 lower, respectively. Changes in pH of protein solution resulted in decrease of association constants in nearly all examined derivatives.