Isolation of PS II reaction centre and its relationship to the minor chlorophyll‐protein complexes

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Abstract
Evidence is presented for the identification of the chlorophyll‐ protein complex CPa‐1 (CP 47) as the reaction centre of photosystem II (PS II). We have developed a simple, rapid method using octyl glucoside solubilization to obtain preparations from spinach and barley that are highly enriched in PS II reaction centre activity (measured as the light‐driven reduction of diphenylcarbazide by 2,6‐dichlorophen‐olindophenol). These preparations contain only the two minor chlorophyll‐protein complexes CPa‐1 and CPa‐2. During centrifugation on a sucrose density gradient, there is a partial separation of the two CPa complexes from each other, and a complete separation from other chlorophyll‐protein complexes. The PS II activity comigrates with CPa‐1 but not CPa‐2, strongly suggesting that the former is the reaction centre complex of PS II. Reaction centre preparations are sensitive to the herbicide 3(3,4‐dichlorophenyl)‐1,1‐dimethylurea (DCMU), but only at much higher concentrations than those required to inhibit intact thylakoid membranes.A model of PS II incorporating our current knowledge of the chlorophyll‐protein complexes is presented. It is proposed that CPa‐2 and the chlorophyll a + b complex CP 29 may function as internal antenna complexes surrounding the reaction centre, with the addition of variable amounts of the major chlorophyll a+b light‐harvesting complex.