A) Tyr21, Gln63 Met106 and Trp104 in AppA in the putative dark state conformation. B) The corresponding residues Tyr8, Gln50, Met93 and Trp91 in Slr1694 in the “Trp91 in” conformation that represents the putative, pseudo-dark state. C) These Slr1694 residues in the “Trp91 out” conformation that represents a putative light-excited state (see text). D) The corresponding residues in Tll0078, also in a putative light-excited state.