Synthesis of a model for phycocyanin with respect to the acid-base chemistry between protein and chromophore

Earlier investigations have shown that the cysteine adduct of phycocyanobil in dimethylester qualifies for intramolecular protonation [1]. In this cont ext, the -Cys-Ala-Phe-Asp-tetrapeptide adduct of phycocyanobilin dimethyles ter was synthesized and examined for its protonation properties with respec t to the zwitterionic interaction between chromophore and protein.