Photosystem diameter

A relatively simple and quick procedure for the isolation of Photosystem I-enriched particles from the thermophilic cyanobacterium Phormidium laminosum, without the use of detergents for solubilization, is described. The procedure involves sonication of cells, centrifugation and DEAE-cellulose chromatography. The particles had an 02 uptake activity of up to 200 pmol 02. mg chlorophyll h 1 and appeared as vesicles of 200 100 nm diameter when observed under electron microscopy. The analysis of the chlorophyll-protein complexes by polyacrylamide gel electrophoresis showed that these particles are enriched in the complexes associated with Photosystem I and partially depleted in those associated with Photosystem II. The particles did not contain ferredoxin and were active in NADP-photoreduction only in the presence of added ferredox in. They were also able to photoreduce externally added electron mediators using ascorbate as electron donor, the reduced mediators can be coupled to hydrogenase for the production of H2 or for the activation of cyanobacterial phosphoribulokinase using a ferredoxin/thioredoxin system. 

The four fracture faces in Pig. 18 (C) show imbedded particles of various sizes. In particular, the EFg face shows a profusion of 16 nm-diameter particles. The complementary fracture face PFs contains relatively tightly-packed, but rather indistinct and smaller particles. It is known that fractionation of a thylakoid membrane disrupted by detergent or by mechanical means yields separate granal and stromal fractions. The granal fraction has been found to be enriched in photosystem-II components and activity. 

Experiments to define the mechanism of anticyanobacterial action of nostocyclamide indicated that the compounds also inhibit chlorophyceans, although less potently. It was shown that Anahaena cyanobacteria were inhibited in the synthesis of chlorophyll a, carotenoids, and protein after 36 h. These filamentous bacteria also formed much shorter filaments than normal, and the cells appeared swollen, with a greater than normal diameter. However, nostocyclamide did not inhibit electron flow through photosystem II, indicating that the compound did not directly target photosynthesis fer se. 

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