Phycobilisome Heterogeneity in the Red Alga Porphyra umbilicalis

Phycobilisomes were isolated from Rhodophyceae brought from the field (Porphyra umbilicalis) or grown in culture under laboratory conditions (Antithamnion glanduliferum). In P. umbilicalis two kinds of well-coupled (ellipsoidal and hemidiscoidal) phycobilisomes were detected, in contrast to A. glanduliferum cultured algae in which only one kind of well-coupled, ellipsoidaltype phycobilisome appeared. The new phycobilisome-type particle detected in P. umbilicalis is characterized by an impoverishment in R-phycoerythrin and by sedimentation at lower density. The comparison between both phycobilisomes of P. umbilicalis allows determination of the presence of one colorless linker polypeptide (30 kilodaltons) associated with R-phycocyanin and allophycocyanin and two (40 and 38 kilodaltons) associated to R-phycoerythrin. The percentage of linker polypeptides associated with this pigment is low in the new phycobilisome-like particle detected. This suggests that part of the R-phycoerythrin is less strongly bound to the phycobilisome than the other pigments. This feature could probably explain the existence of two kinds of phycobilisomes as intermediary steps of phycobilisome organization in algae exposed to rapid changes in environmental factors. In contrast, algae growing in culture and adapted to specific conditions do not present intermediary organization steps. Polypeptide composition and identification are given for this phycobilisome-like particle.