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This paper investigates the polarization effects associated with functional processes in photosynthetic membranes.It is now well established that the primary steps of photosynthesis-a highly efficient electron transfer against the thermodynamic potential gradient-occur in so-called photosynthetic reaction centers (RCS), membrane-bound molecular complexes composed of specific proteins to which porphyrin pigments and some redox cofactors are attached. We used RC preparations extracted from membranes of photosynthetizing bacteria Rhodopseudomonas sphaeroides (1760-1) with the anion-active detergent SDS. The RCS thus obtained contain protein components of total molecular weight of approximately 100 kdaltons, carrying the following prosthetic groups that are needed to accomplish the primary photochemical act: molecules of bacteriochlorophyll (BChl), bacteriopheophytin (BPh), and ubiquinones (UQ); and some nonheme iron Fei2 and carotenoids not removed by detergent [l]. Light activation of RC leads to a rapid transfer of an electron (tl/2 = 200 psec) from the photoactive dimer (BChl)2 to the primary acceptor Q1 which is of a quinone nature [2, 31. Ionradicals (BChl); and Q; do not undergo recombination for at least tens of msec [ l , 41. The stabilization of the primary redox products during this time-which is sufficient for these products to be involved in the functional processes (direct oxidoreductions, generation of the electric potential)-is, probably, provided by means of conformational changes in the RC, following the photochemical act [5]. Such structural rearrangements can occur as a result of electron-conformational interactions involving the polarization of the dielectric surrounding of the primary reactants of RC [6]. As estimated, electric fields thus built up can be as high as 105-106 V/cm. In the photosynthetic membrane there is an intrinsic indicator of the polarized state-light-harvesting pigments; in particular, carotenoids. Fields of above strength shift electron energy levels in such molecules giving rise to the field-induced absorbance changes. As is seen in Figure 1, the spectra of lightinduced and field-induced (5 x 10' V/cm) absorbance changes of carotenoids in dried films of chromatophores Rhodospirillum rubrum are very similar [7]. The electrochromic band shift in absorbance is quadratic in field strength, in agreement with the predictions of Stark's theory for complex molecules of organic dyes without permanent dipole moments. Hence, electric fields, if of appropriate *

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