ABSTRACT
Phycobilisomes are composed of proteins: biliproteins and linker polypeptides. This chapter discusses the covalent chemical structures of the biliproteins isolated from these phycobilisomes. It also discusses the composition of biliprotein subunits, the distribution of bilins (chromophores) among the subunits, the tetrapyrrole structures of the various bilins, the covalent bonding between tetrapyrrole and apoprotein, and the sequences of the amino acids in these biliproteins. Sodium dodecyl sulfate gel electrophoresis experiments first clearly demonstrated the possibility that all the purified biliproteins were composed of at least two subunits. Generally, the lower molecular weight subunit was designated a and the larger ß. Amino acid analysis of the a and ßsubunits of C-phycocyanin showed that they were distinct gene products. High biliprotein concentrations and pH values near 2 promoted retention of chromophore absorbance. Reducing agents like mercaptoethanol or dithiothreitol promoted loss of bilin absorbance.
