31] Phycobiliproteins

Abstract

This chapter focuses on Phycobiliproteins. In intact cyanobacterial cells and red algal chloroplasts, the phycobiliproteins are components of a complex assemblage, the phycobilisome. The observation that upon cell breakage the products of phycobilisome dissociation are released in water-soluble form gave rise to the unfortunate impression that the phycobiliproteins represented a fairly simple family of well-behaved macromolecules. Appraisal of the true complexity of the situation required an understanding of the molecular structure of phycobilisomes. During purification procedures, certain phycobilisome polypeptide components are lost through retention on chromatographic supports, or, in some cases, destroyed by proteolysis. Some phycobiliproteins, such as allophycocyanin B, are products of subunit scrambling during purification procedures, while others, such as the β18.3 polypeptide of the phycobilisome core, which is present in only two copies per phycobilisome, may copurify undetected with one of the major phycobiliproteins such as allophycocyanin. A polypeptide pattern obtained by SDS-polyacrylamide gel electrophoresis is an absolutely essential element in the characterization of a purified phycobiliprotein preparation. A sufficient amount of protein should be applied to the gel to ensure that components present in small amounts are detected.