Binding Interactions of Hematoporphyrin Monomethyl Ether with Bovine Serum Albumin

Hematoporphyrin monomethyl ether (HMME) that is the second generation photosensitizers is a new and promising porphyrin related photosensitizer for photodynamic therapy and diagnosis in certain tumor. The binding of HMME to bovine serum albumin (BSA) in aqueous solution was studied using fluorescence spectra and absorption spectra. It was shown that HMME has a powerful ability to quench the BSA fluorescence by a non-radiative energy transfer mechanism. The binding constants, Kq, at 303 K and 310 K were obtained by fluorescence quenching method and the values were 3.1987 times 10¹² L mol^-1, 3.7156 times 10¹² L mol^-1, respectively. The fluorescence quenching mechanism of BSA by HMME is a dynamic quenching procedure . The critical transfer distance R₀ were calculated (R₀=2.602 nm) based on the theory of Foster spectroscopy energy transfer. The standard enthalpy change (DeltaHdeg)and the standard entropy change (DeltaSdeg) were calculated, which indicated that hydrophobic forces played major role in the interaction of HMME and BSA. The effect of HMME on the conformation of BSA was analyzed by means of synchronous fluorescence spectroscopy.