The apparent non-linearity of the relationship between the rate of respiration and the protonmotive force of mitochondria can be explained by heterogeneity of mitochondrial preparations.

The apparent non-linear relationship between the rate of respiration and the protonmotive force in mitochondria under resting state conditions is an observation which has led to concepts such as non-chute characteristics of the proton leak through the mitochondrial membrane, or a slippage of proton pumps. We propose that this non-linearity may be a consequence of a heterogeneity of isolated mitochondria concerning the degree of coupling, since a small proportion of totally uncoupled, or loosely coupled, organelles may considerably contribute to the total respiration but not, or only slightly, to the protonmotive force. This hypothesis is supported by a fairly good fitting of computed relationships with those determined experimentally.