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The ADP addition containsDuring the initial stimulated interval, the plotted oxygen concentration falls from about $240$ to $207\mu \mathrm{M}$. The chamber volume after this addition is $1.900+0.050+0.050+0.010=2.010\mathrm{mL}$, givingThe conventional phosphorylation-to-oxidation ratio counts ATP formed per oxygen atom reduced, so its denominator is twice the number of oxygen molecules:This assumes the added ADP is phosphorylated and uses the displayed total oxygen loss over the pulse; it is an apparent experimental ratio. A separate correction for background respiration or proton leak would change the denominator and must be specified explicitly. Dividing by oxygen molecules without the factor of two would instead give an ATP:${\mathrm{O}}_2$ ratio near $3$.

At low ATP demand, the proton-motive force is high and much of the remaining oxygen consumption supports proton leak. Increasing leak conductance then creates a substantial extra demand for proton pumping and strongly changes respiratory flux. At high phosphorylation demand, proton return through ATP synthase is large, the proton-motive force is lower, and leak contributes a much smaller part of total proton return. Control of oxygen consumption shifts toward substrate supply and the respiratory machinery, so the leak flux control coefficient becomes small. The plot's value near zero does not mean that the physical leak current vanishes; the separate maximal-rate table likewise gives a small nonzero coefficient, $0.04$.