Buffer effects on electric signals of light-excited bacteriorhodopsin mutants

The effects of glycyl-glycine and bis-tris-propane buffers on the light-exc ited electric signals due to proton motion in the molecule were studied for the bacteriorhodopsin (bR) mutants D38R, D96N, E204Q, R227Q, D85N, D85T, R 82Q/D85N, and D85N/D96N in purple membranes and for delipidated purple memb rane containing the wild-type bR. The results show additional charge motion caused by the buffers in all cases. Arrhenius parameters calculated from t he temperature dependence of the difference signals (with buffer minus with out buffer) are similar to the parameters found for the wild-type bR in the case of these buffers: the values of the activation enthalpies are mostly in the range 25-50 kJ/mol; all the activation entropies are negative. The r esults are evaluated with the cluster hypothesis outlined previously.