MAGNETOPHOTOSELECTION OF THE TRIPLET-STATE OF REACTION CENTERS FROM RHODOPSEUDOMONAS-SPHAEROIDES R-26

Reaction centers of the photosynthetic bacterium R. sphaeroides R-26, give rise to large triplet state EPR signals upon illumination at low temperature (11.degree. K). Utilizing monochromatic polarized light to generate the EPR spectra (magnetophotoselection) showed that the intensities of the observed triplet signals are strongly dependent on the wavelength and polarization direction of the excitation. The orientations of the excited transition moments were calculated with respect to each other and with respect to the triplet state principal magnetic axes system. This quantitative approach follows the procedure outlined in a previous publication where computer simulations of the observed triplet state spectra were employed. Apparently the transition moment at 870 nm which is associated with the bacteriochlorophyll special pair lies almost entirely along one of the principal magnetic axes of the triplet state. The 870 nm transition moment makes an angle of about 60.degree. with the 546 nm transition moment which is associated with a bacteriopheophytin. This latter result is in agreement with previous photoselection studies on the same bacterial species.