Phycocyanin There are 2 extra helices not found in normal globins (gray). These helices mediate the dimeric interaction. The other helices are colored by group, N-terminus blue. The spacefilling group (Phycocyanobilin) occupies a position similar to the heme in myoglobin. Phycocyanin is a bacterial or plant protein involved in photosynthesis. Brejc, K., Ficner, R., Huber, R., Steinbacher, S.: Isolation, crystallization, crystal structure analysis and refinement of allophycocyanin from the cyanobacterium Spirulina platensis at 2.3 A resolution. J Mol Biol 249 pp. 424 (1995) (PubMed) 1all (PDB)