Fig. 4.

Accessibility changes induced by ions and substrate (glycine). The conformational response to ligand binding was estimated by changes in the reactivity of Cys60 in the extracellular pathway and Cys244 in the cytoplasmic pathway toward MTSET added to the medium of intact cells expressing GlyT1b Y60C-C62A (A) or to membranes from cells expressing GlyT1b S244C-C62A (B). (A) Cys60 reactivity. (B) Cys244 reactivity. Asterisks indicate significantly different rate constants (*P < 0.02; **P < 0.01) using Student’s t test. All error bars represent the SEM; n ≥ 4. (C) Conformational response, in the presence of Na⁺, to Cl⁻ or glycine, relative to the response to both. The change in accessibility of Cys60 and Cys244 between Na⁺ alone and NaCl + glycine was set at 100% and the changes induced by Cl⁻ or glycine scaled accordingly. Light gray bars represent cytoplasmic pathway (Cys244) reactivity and dark gray bars, that of the extracellular pathway (Cys60). All error bars represent the SEM; n ≥ 4.