Modified reaction centers from Rhodobacter sphaeroides R 26 Exchange of monomeric bacteriochlorophyll with 1 32 - hydroxy - bacteriochlorophyll

Incubation of photosynthetic reaction centers from Rhodobucter sphaeroides R26 with exogenous lY-OH-bacteriochlorophyll ar or aoo according to Scheer et al. (1987) results in the exchange of endogenous bacteriochlorophyll ar. The exchange amounts to 5 50% according to HPLC analysis, corresponding to a complete replacement of the ‘monomeric’ bacteriochlorophylls, Bu and Br, by exogenous pigment. The absorption spectra show small, but distinct changes in the Qx-region of the bacteriochlorophylls, and bleaching of the modified reaction centers is retained. The corresponding binding sites must be accessible from the exterior, and allow for the introduction of a polar residue at C-1P. This is supported by the observation of side reactions of the endogenous ‘monomeric’ bacteriochlorophylls within the reaction center pigments, e.g. epimerization and hydroxylation at C-l32.