[Characteristics of complex-formation of chlorine e6 with human and bovine serum albumins]

Pigment-protein complexes of chlorin e6 (Chl e6) with human (HSA) and bovine serum albumines (BSA) have been investigated by spectral-luminescent methods. Fluorescence quenching of tryptophan residues caused by the inductive-resonance energy transfer to pigment molecules and the rise of the polarization degree of Chl e6 emission were observed upon incorporation of Chl e6 in the protein globula. The obtained data on spectral-energetic parameters of protein tryptophanyls and Chl e6 permitted us to calculate the energy transfer critical distances R0 in complexes of Chl e6 with HSA (R0 = 32 A) and BSA (R0 = 35A). The binding constants (K) and the number of binding sites (N) of Chl e6 with HSA and BSA have been obtained from the experiments on tryptophanyl fluorescence quenching of the investigated proteins and polarization measurements of pigment emission (KHSA = 1.2.10(6) mole-1, KBSA = 3.6.10(6) mole-1, NHSA = NBSA = 1). On the basis of the measured values of electronic excitation energy transfer efficiency (phi greater than or equal to 99%) the average distances between the protein chromophores and the incorporated Chl e6 molecules have been calculated (RHSA = 15-17 A, RBSA = 16.5-18 A). The questions connected with pigment localization sites in the protein globula and specific features of pigment-protein interaction are discussed.