Photochemistry and electron transfer in borohydride-treated photosynthetic reaction centers

The photochemistry and electron-transfer activities of sodium-borohydride-treated reaction centers from the purple photosynthetic bacterium Rhodopseudomonas sphaeroides R26 have been investigated by both milliand picosecond absorption techniques. Separation from the treated reaction center of the reduction product, apparently a reduced form of one of the two molecules of bacteriochlorophyll contributing to the 800 nm ground-state absorption band, is also reported. In the near-infrared region, differences between treated and untreated reaction centers are observed in both milli- and picosecond light-induced difference spectra. However, borohydride-treated reaction centers exhibit photochemistry and electron transfer which are indistinguishable from those observed in untreated reaction centers. These results indicate that normal activity occurs in reaction centers that contain both molecules of bacteriopheophytin, but only three of the usual four molecules of bacteriochlorophyll.