Core substructure in phycobilisomes of red algae. II. The central part of the tricylindrical core--APCM--a constituent of hemidiscoidal phycobilisomes of Rhodella violacea.

The central part of the tricylindrical core of phycobilisomes from Rhodella violacea was isolated by hydroxylapatite adsorption chromatography followed by density gradient centrifugation. In the electron microscope negatively stained APCM complexes showed a tricylindrical face view with an edge length of 20 to 24 nm and a thickness of 9 to 10 nm in profile view. These complexes had a M(r) of 900,000, and a sedimentation coefficient 24S. The fluorescence emission maximum at room temperature lay at 671 nm when excited at 590 nm. The presence of the high molecular linker polypeptide LCM exclusively in APCM and the existence of beta AP19.5, alpha AP18, and beta AP17 were demonstrated in SDS-polyacrylamide gel electrophoresis. The presence of "trimeric" allophycocyanin complexes in a separate band, with a sedimentation coefficient 6S, confirms the uncoupling of these complexes from the core; their maximal fluorescence at 680 nm in the second derivative hints at alpha AP-8. The results indicate a high conformity in the molecular organization of the core of hemidiscoidal phycobilisomes of red algae (Rhodella violacea) and cyanobacteria (Mastigocladus laminosus).