Models of pigment-protein interactions in photosynthetic systems: Tetraphenylporphyrin complexes with polycationic sequential polypeptides. Absorption, circular dichroism and fluorescence properties

Abstract

Absorption and circular dichroism spectra and steady state and time-resolved fluorescence of complexes of 5,10,15,20-tetrakis (4-carboxyphenyl)porphyrin with sequential helical polypeptides (L-Lys-L-Ala) n , (L-Lys-L-Ala-L-Ala) n , and (L-Lys-L-Ala-L-Ala-L-Ala) n are studied. Changes of electronic transition energies, induction of optical activity and two-component fluorescence decay with components t 1 = 2–3 ns and t 2 = 180 ps characterize the complexed pigment. Dependence of these changes on relative number of lysine amino acids in polypeptide primary structures was observed and is discussed in terms of perturbational influence of polypeptide molecular field on mixing of porphyrin electronic states.