ORIGIN OF THE RED SHIFTED ABSORPTION IN PHYCOCYANIN 632 FROM <i>Mastigocladus laminosus</i>

Abstract

Abstract A phycocyanin (PC) with γ max = 632 nm (PC632) was isolated from extracts of the cyanobacterium Mastigocladus laminosus. The complex contained three polypeptides migrating in SDS‐PAGE around 22 kDa. The N‐termini of the three polypeptides are identical. They are homologous to rod‐core linker polypeptides from this and another cyanobacterium and are identical to one of them. Reconstitution of PC (γ max =614–620 nm) with the 22 kDa polypeptide produced again the red‐shifted PC632. Phycobilisomes isolated at pH 6 or 7 contain, if any, only traces of 22 kDa polypeptides. Origin and functions of the polypeptides are discussed, they are most likely proteolytic fragments of allophycocyanin‐PC rod‐core linkers that contain the PC‐binding domain.