FIGURE 4.

Modulation of thiol-reactive reagent-dependent inhibition by pH. A, effect of NEM incubation (1 mm for 2 min) on activity of F179C and H183C incubated at pH 7.0 and pH 5.5 in absence of substrate. B, effects of MTSET incubation (0.2 mm for 2 min) at pH 7.0 (left) and pH 5.5 (right) in the absence of substrate. For all experiments, pretreatment was for a total of 10 min: the first 8 min at the indicate pH alone and the final 2 min at the same pH with NEM or MTSET. For transport measurements, the concentration of NANA was 30 nm, and the reaction was terminated at 5 min. **, p < 0.01.