Magnetic field effects on the fluorescence of mutant strains of Rhodopseudomonas capsulata

The magnetic field effects on bacteriochlorophyll fluorescence in six strains of Rhodopseudomonas capsulata were investigated. All strains exhibit an increase in fluorescence upon application of a magnetic field. Large magnetic field effects are shown to arise in mutants which contain the B800–850 complex as the only bacteriochlorophyll-containing protein. These fluorescence increases are observed only with carotenoid excitation and are best described by a carotenoid singlet heterofission mechanism. Variations in the magnitudes of the magnetic field effects for the Rps. capsulata strain arise from energy differences in the excited states of the molecules involved in the process. In order to determine the contribution from reaction centers to the magnetic field effects observed in the mutants which contain all three pigment-protein complexes, reaction centers were isolated from these strains. The reaction center contribution to the magnetic field effect on fluorescence in whole cells was determined to be smaller than the antenna contribution when carotenoid excitation was employed.