Fig. 3.

Role of S_m site residues in urea flux and osmosensing. (A) Averaged, background-corrected traces showing the change in fluorescence over time from quenching of entrapped dye in WT (red), T334V (violet), and T334S (blue) UT-B-containing proteoliposomes and control liposomes (black), driven by urea efflux, scaled to the theoretical change in volume. (B) Initial rates of urea efflux calculated from these curves and for additional mutants. Errors bars are standard deviations from three or four experiments. (C) ¹⁴C-labelled urea uptake in WT or T172S/T334S UT-B mRNA-injected oocytes or in control oocytes after 5 min placed in ND-96 buffer at 0.5, 1.0, and 2.0-fold concentration.