REACTION CENTERS OF RHODOBACTER-SPHAEROIDES R26 CONTAINING C-3 ACETYL AND VINYL (BACTERIO)PHEOPHYTINS AT SITES H-A,H-B

The native bacteriopheophytin a in reaction centers of Rb. sphaeroides R26 has been exchanged with modified bacteriopheophytins (bacteriochlorins), as well as with plant-type pheophytins (chlorins). Emphasis is on four pigments, which differ by their C-3 substituents (vinyl or acetyl) or their state of oxidation (chlorin or bacteriochlorin). The native BPhe a, which is a member of this group, can be replaced by the other three at both binding sites, H-A and H-B. However, exchange at H-B proceeds more readily. Optical spectra (absorption, cd) show characteristic shifts, and the ed spectra indicate induced interactions between H-A,H-B and B-A,B-B and possibly also with P. Upon flash illumination, all modified reaction centers show reversible electron transfer to Q(B) with recombination times comparable to native reaction centers. Forward rates and electron-transfer yields are also reported for some of the pigments.