Ultrafast Electron Transfer in Modified Photosynthetic Reaction Centers from Rhodobacter Sphaeroides Measured by Fluorescence Upconversion

Abstract

In photosynthetic reaction centers determination of ultrafast electron transfer rates as a function of the thermodynamical driving force ΔG allows conclusions on the mechanism of primary charge separation. In this paper we present femtosecond timeresolved fluorescence measurements on the primary donor species P* in reaction centers from Rhodobacter Sphaeroides R26 after modifying the energetics of the neighboring pigment, a bacteriochlorophyll molecule. The modification was achieved by thermally replacing the pigment by a specially designed derivative, the Ni-bacteriochlorophyll. Room temperature rates for the primary charge separation in the modified reaction centers are the same as in the native ones. This supports a sequential two step mechanism also in native reaction centers.