Topology of pigments in the isolated Photosystem II reaction center studied by selective extraction

Pigments in the purified spinach Photosystem II reaction center (D1-D2-Cyt b-559) complex were extracted with diethyl ether containing varied amounts of water. The purified reaction center originally contained approximately six molecules of chlorophyll a, two beta-carotene and two pheophytin a per one photochemically active pheophytin a. The treatment with 30-50% water-saturated ether extracted one beta-carotene, as well as one chlorophyll a that absorbs at 677 nm, remaining 62% of the photochemical activity to reduce pheophytin a, With 60-80% water-saturated ether, almost all the beta-carotenes were extracted, remaining the 49% activity without additional loss of chlorophyll. The absorption, fluorescence excitation and linear dichroism spectra demonstrated two spectral forms of beta-carotene. The short-wavelength form of beta-carotene with absorption peaks at 429, 458 and 489 nm was selectively extracted with ether at low water content, whereas the long-wavelength form with peaks at 443, 473 and 507 nm was extractable only at the higher water content. The extraction enhanced the photobleaching of chlorophylls. The results suggest that chlorophyll a forms with peaks at 667 and 675 nm are located close to the short-wavelength form of beta-carotene that can transfer excitation energy to the photoactive pheophytin a on the D1 protein. (C) 1997 Elsevier Science B.V.