“…In purple membranes, but not in the monomers, the photocycle, which describes the sequence of intermediate states (termed J, K, L, M, N, and 0) after photoexcitation of the retinal chromophore with a light pulse, exhibits distinct kinetic differences when the intensity of the actinic laser beam is varied. The differences consist mainly of what appears to be an increase in the amplitude, although not the time constant, of the slower component in the biphasic decay of the M intermediate at pH near 9 (Tokaji and Dancshazy, 1992; Dancshazy and Tokaji, 1993;Tokaji, 1993Tokaji, , 1995Hendler et al, 1994;Mukhopadhyay et al, 1994;Shrager et al, 1995). Thus, the excitation intensity can evidently influence not only the number of bacteriorhodopsins that are photoexcited but also the rate of at least one of the steps in the proton transport.…”