Fig. 5.

ATPase hydrolysis (i.e., K⁺ net flux) as a function of luminal pH in Na⁺- and NH₄⁺-free medium. We simulated Fig. 2 in Ref. 43 using our ATPase mathematical model (Eq. 1) with Weinstein's (43) and Brzezinski et al. (6) model parameter sets in Table 2 (continuous lines). We also show simulations with our nongastric HKA model parameter sets in Table 2 (dashed lines). ATP hydrolysis was computed using Eq. 6. Plots were zoomed to appreciate small-scale ATPase activities. K⁺ flux reverses at a pH_l of ∼2.77 for our 2H⁺:2K⁺-per-ATP model and at a pH_l of ∼3.33 for Weinstein's 2H⁺:2K⁺-per-ATP model (solid circles).