Characterisation of a PS II reaction centre isolated from the chloroplasts ofPisum sativum

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Abstract
A photosystem II reaction centre has been isolated from peas and found to consist of D1, D2 polypeptides and the apoproteins of cytochromeb‐559, being similar to that reported for spinach by Nanba and Satoh [(1987) Proc. Natl. Acad. Sci. USA 84, 109–112]. The complex binds chlorophylla, pheophytin and the haem of cytochromeb‐559 in an approximate ratio of 4:2:1 and also contains about one molecule of β‐carotene. It binds no plastoquinone‐9 or manganese but does contain at least one non‐haem iron. In addition to a light‐induced signal due to Pheo−seen under reducing conditions, a light‐induced P680+signal is seen when the reaction centre is incubated with silicomolybdate. In the presence of diphenylcarbazide, the P680+signal is partially inhibited and net electron flow to silicomolybdate occurs. This net electron flow is insensitive too‐phenanthroline, 3‐(3,4‐dichlorophenyl)‐1,1‐dimethyl urea and 2‐(3‐chloro‐4‐trifluoromethyl)anilino‐3,5‐dinitrothiophene but is inhibited by proteolysis with trypsin and by other treatments. Fluorescence, from the complex, peaks at 682 nm at room temperature and at 685 nm at 77 K. This emission is significantly quenched when either the P680+Pheo or P680Pheo−states are established indicating that the fluorescence emanates from the back reaction between P680+and Pheo−.