Figure 3
Mutational effects of carboxylates on proton transport activity. (A) Light-induced pH changes of suspensions of E. coli cells expressing AR3, wild-type RxR and mutants of RxR in the absence or presence of the protonophore, CCCP (red and blue, respectively) in NaCl solution. The suspensions were illuminated with yellow light (>480 nm) for 3 min (white background). As a negative control, E. coli cells harboring the pET22b vector were used. Aligned images on the right show E. coli cells expressing AR3, wild-type RxR and mutants of RxR. The amplitudes of pH changes for D74N, D85N and D205N were enlarged by 3 times for the comparison. (B) Quantitative evaluation of the proton pumping activities of AR3, wild-type RxR and mutants of RxR. The initial slope amplitudes of the light-induced pH changes in NaCl solution, which were obtained from the data in panel A, were normalized against the total amounts of photoactive proteins (Fig. S4). All error bars represent standard error of the mean (SEM) of three independent measurements (n = 3). Asterisks (*) indicate a significant difference from wild-type RxR (P < 0.05; Dunnett’s test). NS indicates no significant difference (P > 0.05; Dunnett’s test).
