Interactions of chlorophyll a with synthesized peptide in aqueous solution

The interactions between chlorophyll a and synthesized peptides have been studied using optical spectroscopy. Three 30-residue peptides are designed and synthesized: an amphiphilic peptide without histidine (L), an amphiphilic peptide with histidine (L/H) and a hydrophilic peptide (K/E). These peptide properties thereby allow us to examine the effect of the peptide hydrophobicity and/or histidine residue on pigment-peptide interactions. On mixing with peptides, chlorophyll a has a main absorption band in the Qy region with the maximum at 672 nm. For all three peptides, fluorescence patterns show that at a low concentration of the peptide (0.05 mM) in aqueous solution, the energy is transferred among various forms of the pigment. Only peptide L/H at high concentration (0.5 mM) in solution retains the Qy band of chlorophyll a at 672 nm, and the emission is that typically seen for the monomeric form of the pigment. The aggregation of chlorophyll a is suppressed most strongly in the presence of the peptides L/H. The results suggest that chlorophyll a is ligated to a histidine residue, located in the hydrophobic region of the peptides L/H, and in surrounded or shielded by the peptide alpha-helixes.