Phycobilisome Structure of Porphyridium cruentum

Abstract

Purified phycobilisomes of Porphyridiwm cruentum were solubilized in sodium dodecyl sulfate and resolved by sodium dodecyl sulfate-acrylamide gel electropboresis into nine colored and nine colorless polypeptides. The colored polypeptides accounted for about 84% of the total stainable protein, and the colorless polypeptides accounted for the remaining 16%. Five of the colored polypeptides raning in molecular weight from 13,300 to 19,500 were identified as the a and ,8 subunits of aflophycocyanin, R-phycocyanin, and phycoerythria Three others (29,000-30,500) were orange and are probably related to the y subunit of phycoerythrin. Another colored polypeptide had a molecular weight of 95,000 and the characteristics of long wavelength-emitting aBophycocyanin. Sequential dissociation of phycobilisomes, and analysis of the polypeptides in each fraction, revealed the association of a 32,500 molecular weight colorless polypeptide with a phycoerythrin fraction. Tne remaining eight colorless polypeptides were in the core fraction of the phycobilisome, which also was enriched in allophycocyanin. In addition, the core fraction was enriched in a colored 95,000 dalton polypeptide. Inasmuch as a pobpeptide with the same molecular weight is found in thylakoid membranes (free of phycobilisomes), it is suggested that this polypeptide is involved in anchoring phycobilisomes to thylakoid membranes.

One-step chromatographic procedure for purification of B-phycoerythrin from Porphyridium cruentum

“…The analysis by SDSePAGE revealed a broad band between 18 and 20 kDa which could be assigned to subunits a and b and a low intensity band of 31 kDa assigned to g subunit (Fig. 4B), which consistents with the value reported previously [9,28,38,39].…”

Photosynthetic Membranes of Porphyridium cruentum

“…Thus, we can now conclude that the Chl previously assumed to be associated with the 95,000 D polypeptide was contributed by some of the CP III which had not been separately resolved. Our previous observation (23,24) on the presence ofChl with the blue-colored 95,000 D polypeptide from isolated phycoblisomes remains unaffected by our present findings.…”

“…Thylakoids were free of phycobilisomes as determined by electron microscope examination and by A540/A675 < 0.05. All buffer solutions were as previously given (23,24 were recorded at -196°C on an Aminco-Bowman spectrofluorometer in the quantum corrected mode. Samples were isolated from polyacrylamide gels (21) and dialyzed against 50 mm Naphosphate buffer (pH 7.5) and 20% glycerol (v/v) prior to spectral analysis.…”

“…Thylakoid membranes were isolated from cells disrupted with a French pressure cell (5000 p.s.i.) and washed free ofphycobilisomes and other surface binding proteins as described in Redlinger and Gantt (23,24). Purification of thylakoids was by flotation centrifugation (3).…”

Formation of hybrid phycobilisomes by association of phycobiliproteins from Nostoc and Fremyella

“…The presence of a Mr 95,000 polypeptide in both Fremyella and Nostoc as well as in Pseudanabaena (11) is noteworthy, especially since it may be similar to that found in the core fraction of Porphyridium cruentum phycobilisomes and may function as an anchor protein (23). The in vitro-association studies are only in their beginning stages, and it would be premature to draw any phylogenetic conclusions from these results.…”