Quantitative model for the cooperative interaction of the bacteriorhodopsin molecules in purple membranes

The trimeric, asymmetric and sequential model for the cooperative interaction of the bacteriorhodopsin molecules in purple membranes [Zs. Tokaji, Biophys. J. 65 (1993) 1130-11341 is being extended in the paper. Analyses of data from absorption kinetic measurements with preexcitation and green background illumination, and photoselection measurements on oriented samples confirm the main features of this cooperative interaction and support the validity of the extended model. This model includes the observed heterogeneity of the non-excited state of the bacteriorhodopsin molecules in purple membranes, and the agreement with the data suggests that molecules in any other state than the bacteriorhodopsin ground state can alter the photocycle of their neighbors. The presented results seem to contradict other models for the cooperation of the bacteriorhodopsin molecules.