Characterization of a Purified Photosystem II-Phycobilisome Particle Preparation from Porphyridium cruentum

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Abstract
Detergent preparations isolated from thylakoids of the red alga, P. cruentum, in a sucrose, phosphate, citrate, magnesium chloride medium consist of phycobilisomes and possess high rates of photosystem II activity. Characterization of these particles shows that the O2-evolving activity is stable for several hours and the pH optimum is .apprx. 6.5-7.2. Response of the system to light, electron donors and acceptors, and inhibitors verify that the observed activity, measured both as O2 evolution and 2,6-dichlorophenol-indophenol reduction, is due to photosystem II. Photosystem II is functionally coupled to the phycobilisome in this preparation since green light, absorbed by phycobilisomes of P. cruentum, is effective in promoting both O2 evolution and 2,6-dichlorophenol-indophenol reduction. Photosystem II activity declines when light with wavelengths < 665 nm is removed. Both 3-(3,4-dichlorophenyl)-1,1-dimethylurea and atrazine inhibit phostosystem II activity in this preparation, indicating that the herbicide binding site is a component of the photosystem II-phycobilisome particle.