Top: Cartoon view of two subunits of GLIC, all the sites of bimane labeling are represented by a colored sphere. (A, B, C, D, E, F): The data show the fluorescence peak values as a function of the proton concentration, normalized to the peak intensity after SDS treatment. The same color code as the top cartoon was used to indicate the site of bimane labeling for each graph. Within one graph, the major quenching pairs with or without quencher are shown in bold black caption and secondary tryptophan quenchers are captioned in grey. The symbol ø was used for recordings made on receptors baring no other mutation than the one for bimane labeling and for which no endogenous quenchers were identified; otherwise the later are indicated in bold black caption. For all the points, mean values are presented and error bars represent the standard deviations.