Spectroscopic characterization of reaction center crystals from the carotenoid-containing wild-type strain Rhodobacter sphaeroides Y

AbstractThin three-dimensional crystals of the photochemical reaction center from Rhodobacter sphaeroides wild-type strain Y were investigated with microspectrophotometric methods. Absorbance and linear dichroism spectra were obtained for two crystal forms with the same type of unit cell, but grown in different morphological forms. High dichroism was found for the Qx and the Qy transitions of the bacteriopheophytin as well as for the Qy transitions of the accessory bacteriochlorophylls and the bacteriochlorophylls forming the primary electron donor. Low absorption and dichroism of the carotenoid transitions in the plane of the crystal suggests a large component out of the crystal plane. Photoactivity of the crystal was demonstrated by light-induced charge separation. The analysis of the rates of charge recombination indicates that almost all reaction centers in the crystal (> 90%) contain the secondary electron acceptor QB