FIGURE 5.

Saturation kinetics of the photoinduced Cl⁻ pump activity of pHR. (A) Representative I-V curve at steady state in pHR-expressing oocytes at increasing concentrations of Cl⁻ (as NaCl) (1–100 mM). (B) Photoinduced currents at −50 mV indicative of Cl⁻ entry as a function of Cl⁻ concentration. The experiment was repeated five times with different oocytes. Since the expression levels of pHR varied among the oocytes, data were normalized by the value of I_max, calculated using Eq. 1, in each oocyte. The inset shows the Eadie-Hofstee plot. The K_0.5 and I_max values calculated with a Michaelis-Menten-type equation (Eq. 1) were 24.0 ± 2.5 mMand 324 ± 22 nA, respectively. Data represent the mean ± SE (n = 5).