The effect of an electric field has been measured on the absorption spectrum (Stark effect) of the heterodimer mutant (M)H202L of Rhodobacter sphaeroides reaction centers, where the primary electron donor consists of one bacteriochlorophyll a and one bacteriopheophytin a. The electronic absorption spectrum of the heterodimer mutant from 820-950 nm is relatively featureless in a poly(vinyl alcohol) film, but it exhibits some structure in a glycerol/water glass at 77 K. A feature is seen in the Stark effect spectrum of the heterodimer at 77 K centered at 927 and 936 nm in poly (vinyl alcohol) and a glycerol/water glass, respectively. This feature has approximately the same shape and width as the Stark effect for the primary electron donor of the wild type, which consists of a pair of bacteriochlorophyll a molecules. The angle ζA between the transition moment at the frequency of absorption and the difference dipole ΔμA is 36 ± 2° in the wild type and 32 ±2° for that feature in the heterodimer. A range of values for |ΔμA| = (13-17)/f Debye units (where f is the local field correction) is obtained for the 936-nm feature in glycerol/water, depending on analysis method. This feature is interpreted as arising from a transition to the lower exciton state of the heterodimer, which is more strongly mixed with a low-lying charge transfer transition than in the wild type.
|Original language||English (US)|
|Number of pages||5|
|Journal||Proceedings of the National Academy of Sciences of the United States of America|
|State||Published - 1990|
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