Circular Dichroism of the 1300-nm Band of Oxidized Reaction Centers from Rhodopseudomonas viridis†

Reaction centers were prepared from the purple nonsulfur bacterium Rhodopseudomonas viridis, which contains bacteriochlorophyll b. Absorption and circular dichroism (CD) spectra were recorded from 900 to 1360 nm for reaction centers in three states: (I) untreated (cytochromes and P960 reduced), (II) ferricyanide partially oxidized plus light (cytochromes oxidized and P960 80-90% oxidized), and (III) ferricyanide oxidized in the dark (cytochromes oxidized and P960 80-90% oxidized). The absorption and circular dichroism bands of oxidized P960 at ca. 1300 nm were the same in position, shape, and sign (+) for both the chemically oxidized and photochemically oxidized samples. The shape of the 1300-nm CD band is similar to that of the absorption spectrum; there is no indication of "exciton splitting". The relatively high anisotropy ratio of ca. 10-3 should be useful in assigning the electronic states responsible for this transition.