Core substructure in Mastigocladus laminosus phycobilisomes - II. The central part of the tricylindrical core - AP - contains the "anchor" polypeptide and no allophycocyanin B

A native high molecular complex (M 850000) containing about 50% of the allphycocyanin of the phycobilisome but lacking allophycocyanin B was separated from isolated phycobilisomes by gel electrophoresis. It was designated AP since the large linker polypeptide L was exclusively localized in this complex. The complex exhibited a -196°C fluorescence emission maximum at 673 nm (671 nm at 25°C). In addition, a core complex (designated AP, M≥1000000) consisting of both AP and AP 680 was isolated by combined gel filtration and linear gradient centrifugation. At 25°C this complex showed dual emission peaks at 670 and 680 nm demonstrating functional independence of the terminal emitters. A complex similar to AP can be isolated from phycobilisomes of Anabaena variabilis. This is evidence that AP is the constitutive center of the tricylindrical core of hemidiscoidal cyanobacterial phycobilisomes. Two models summarizing the structural and functional consequences of the results are presented in the discussion. © 1990 Springer-Verlag.