Biliproteins: Some Relationships Among Aggregation States, Spectra, and Excitation‐Energy Transfer

The key aggregation steps for C‐phycocyanin consist of denatured subunits (α and β polypeptide chains), monomers, trimers, hexamers and stacks. For allophycocyanin the steps are denatured subunits, monomers and trimers. Ultimately these assembly states lead to the formation of phycobilisomes in blue‐green and red algae. The spectroscopic changes that accompany each stage in the assembly can be monitored as a function of the ratio of visible to near‐UV absorption. For C‐phycocyanin, monomers and hexamers are the important levels in the modulation of tetrapyrrole conformation by protein‐chromophore interaction. The effect of protein aggregation on the protein‐chromophore interactions is the key to solar‐energy harvesting and excitation‐energy migration in photosynthesis.