Affinity of Phycocyanin Chromopeptides to Histidyl-Sepharose Gels: A Model for Histidine-Tetrapyrrol-Interactions in Biliproteins

Abstract

C-Phycocyanin from the cyanobacterium Spirulina m axim a was digested with pepsin to yield chromopeptides and colorless peptides. This mixture was applied to columns of histidyl-Sepharoseunder a variety of conditions (pH-value, ionic strength of buffer). We found a good separation of several chromopeptides from each other and from colorless peptides due to differential interaction of phycocyanobilin chromophore with the histidyl residue of the gel. The separation is suppressed by the use of imidazole buffer. Control experiments were perform ed with purified chromopeptides and with octyl-Sepharose and DEAE-Sepharose. The nature of interaction which probably involves charge transfer interaction besides hydrophobic and ionic forces is discussed with regard to the significance for phytochrome