Studies on the Phycobiliprotein Complexes from the Red Algae Porphyridium cruentum

Abstract

As with cyanobacteria, the red alga Porphyridium cruentum contains large extramembraneous light-harvesting antennae known as phycobilisomes. The architecture of some types of phycobilisoraes, from cyanobacteria as well as from the red alga Rhodella violacea, are well known as a result of electron microscopic studies. The detailed electron microscopic study of these phycobili somes has been made possible by their disc-shaped structures (1). The phycobilisome of Porphyridium cruentum is relatively large (up to 15✫106 Da) and its shape has been described as a large semi-ellipsoid through electron microscopic studies (2). As a result of its shape and size, detailed insight into the substructures of the P. cruentum phycobilisome has not been possible through the use of electron microscopy. Most of the phycobiliproteins of the P. cruentum phycobilisome have already been isolated and described (3,4) As well, the linker-polypeptide composition of the whole phycobilisome was been studied by SDS-polyacrylamide gel electrophoresis (SDS-PAGE). (5). The assignment however of the different linker-polypeptides to the various phycobilisome subcomplexes, especially to the core complexes, is not exactly known. The most abundant phycobiliprotein in the phycobilisome of P. cruentum is B-phycoerythrin (BPE). It is present as a large complex with the composition (αβ)6γ.