Reaction centers of photosystem II with a chemically-modified pigment composition: exchange of pheophytins with 13(1)-deoxo-13(1)-hydroxy-pheophytin a

Isolated reaction centers of photosystem II with an altered pigment content were obtained by chemical exchange of the native pheophytin a molecules wi th externally added 13(1)-deoxo-13(1)-hydroxy-pheophytin a. Judged from a c omparison of the absorption spectra and photochemical activities of exchang ed and control reaction centers, 70-80% of the pheophytin molecules active in charge separation are replaced by 13(1)-deoxo-13(1)-hydroxy-pheophytin a after double application of the exchange procedure. The new molecule at th e active branch was not active photochemically. This appears to be the firs t stable preparation in which a redox active chromophore of the reaction ce nter of photosystem II was modified by chemical substitution. The data are compatible with the presence of an active and inactive branch of cofactors, as in bacterial reaction centers, Possible applications of the 13(1)-deoxo -13(1)-hydroxy-pheophytin a-exchanged preparation to the spectral and funct ional analysis of native reaction centers of photosystem II are discussed, (C) 1999 Federation of European Biochemical Societies.