Cyanobacterial photosystem I: Morphology and aggregation behavior

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Abstract
A simple procedure is described for the preparation of cyanobacterial photosystem I particles with a full complement of antenna chlorophyll a from Triton X-100-solubilized thylakoid membranes. In the presence of .gtoreq. 0.1% Triton X-100, photosystem I particles from Synechococcus 6301 were largely monodisperse. These particles, when negatively stained, appeared to approximate prolate ellipsoids 18 .times. 8 nm. A value of 4-5 .times. 10-19 cm3 was estimated for the volume of the stain-exclusion envelopes of the particles. At low concentrations of Triton X-100, photosystem I particles formed linear aggregates or sheets one-layer thick. The manner of aggregation was strongly dependent on protein concentration. Shadowed preparations of the sheets indicated a thickness of 8.0-8.5 nm.