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 varie d amounts of water. The purified reaction center originally contained approximately six molecules of chlorophyll a, two beta-carotene and tw o pheophytin a per one photochemically active pheophytin a. The treatm ent 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-satu rated ether, almost all the beta-carotenes were extracted, remaining t he 49% activity without additional loss of chlorophyll. The absorption , fluorescence excitation and linear dichroism spectra demonstrated tw o spectral forms of beta-carotene. The short-wavelength form of beta-c arotene with absorption peaks at 429, 458 and 489 nm was selectively e xtracted with ether at low water content, whereas the long-wavelength form with peaks at 443, 473 and 507 nm was extractable only at the hig her water content. The extraction enhanced the photobleaching of chlor ophylls. The results suggest that chlorophyll a forms with peaks at 66 7 and 675 nm are located close to the short-wavelength form of beta-ca rotene that can transfer excitation energy to the photoactive pheophyt in a on the D1 protein. (C) 1997 Elsevier Science B.V.