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ed e 1 The function of three types of bacteriorhodopsins was compared: the wild-type, the bleached and retinal reconstituted and retinal defi-The retinal protein bacteriorhodopsin (BR) acts as a acceptor Asp 85. This transporting photocycle is formed from a succession of intermediates (noted by K, L, M, N After absorbing the light, a charge separation along the sibility of the Schiff-base changes from the extracellular to the cytoplasmic side [13]. The Schiff-base is reprotonated by the proton donor Asp 96 on the cytoplasmic side, reflected by the appearance of intermediate N. In the N to O to BR transition, the retinal reisomerizes to its original all-trans form, a proton is taken up from the * Corresponding author