Chromophore Content of Blue-Green Algal Phycobiliproteins

Abstract

The chromophore content of blue-green algal phycocyanin and allophycocyanin, derived from a unicellular blue-green alga of Synechococcus sp., has been determined by quantitative spectrophotometry. Phycocyanin carries three covalently bound phycocyanobilin chromophores per monomer (molecular weight 36,700). Two of these chromophores are attached to the β subunit and one to the α subunit. Allophycocyanin has a single chromophore per polypeptide chain (molecular weight 16,500). Experiments with blue-green algae belonging to other taxonomic groups (Aphanocapsa sp. and Anabaena sp.) indicate that this chromophore distribution holds generally among cyanophytan phycobiliproteins. Bennett and Bogorad ((1971) Biochemistry 10, 3625) have reported earlier that 3 molecules of phycoerythrobilin are bound per monomer of cyanophytan phycoerythrin, two on the β subunit and one on the α subunit. The present work completes the assignment of the distribution of the chromophores among the blue-green algal phycobiliproteins and their subunits.