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Biophysical comparison of ATP-driven proton pumping mechanisms suggests a kinetic advantage for the rotary process depending on coupling ratio

Fig 5

Free energy landscape for rotary and alternating access mechanisms.

Free energy (FE) calculated using Eq (5) for a representative set of parameters from the optimization protocol, and typical physiological conditions. See S1 File. The steps in the proton pumping cycle correspond to those in Fig 2, with labels. “+ATP” is the ATP binding step, “->ADP” the ATP to ADP hydrolysis step, “-Pi” and “-ADP” the Pi and ADP unbinding steps, “+H+” the H+ binding step on the cytosol side, and “-H+” the H+ unbinding step on the “out” side of the membrane. For the example shown, the maximum FE climbs are 3.1 and 6.7 kcal/mol for the rotary and alternating access mechanisms, respectively, with corresponding rates of 42 and 10 H+/s, for the same driving potential ΔGdriv based on conditions described in S1 File.

Fig 5