Structure and Phycobiliprotein Composition of Phycobilisomes From Griffithsia Pacifica (Rhodophyceae)1

Phycobilisomes in Griffithsia pacifica are closely spaced on the thylakoid membrane. By negative staining, attached and isolated phycobilisomes have been shown to have a block shaped appearance. They are 63 nm long, 38 nm high, and 38 nm wide, making them the largest thus far reported. Isolated phycobilisomes, shown to be functionally intact by their 675 nm fluorescence emission (excitation 545 nm) were stable for more than a day. Phycobiliproteins from dissociated phycobilisomes, separated on sucrose gradients and by polyacrylamide electrophoresis, yielded large (R‐) and small (r‐) molecular weight species of phycoerythrin (ca. 4:1 respectively) constituting 89% of the phycobiliprotein content, with R‐phycocyanin 8%, and allophycocyanin 3% accounting for the rest. Phycobilisomes of Griffithsia pacifica and Porphyridium purpureum (Bory) Drew and Ross (P. cruentum) are structurally very similar with phycoerythrin being on the outside and surrounding a core of R‐phycocyanin and allophycocyanin.