ON THE MOLECULAR-ORIGIN OF THE PROTEIN CATALYSIS OF THE PRIMARY PROCESS IN BACTERIORHODOPSIN PHOTOSYNTHESIS - RETINAL PHOTOISOMERIZATION

Using subpicosecond transient optical absorption spectroscopic techniq ues, the photoisomerization rates and quantum yields were determined f or. bacteriorhodopsin, its relevant mutants, its dionized form and at different pH and Cl- concentrations. It is found that the rate is cata lyzed and made highly specific around the C-13-C-14 bond by the presen ce of negative charges within the retinal cavity (e.g., Asp85 and Asp 212). Any perturbation that genetically removes, acid neutralizes, or changes the geometry of these negative charges is found to decrease th e tate of photoisomerization, but does not greatly change its quantum yield. These results sue discussed in terms of the changes in the elec tronic structure of the retinal as well as in the anisotropic charge d istribution within the cavity that result from the photoexcitation pro cess. The different potential energy surfaces proposed to explain the dynamics of the photoisomerization process are examined in terms of ou r observed results.