Biochemical threshold effect
Due to threshold effects, even a large defect diminishing the velocity of an individual enzyme results in only minor changes of pathway flux.
Reference: Gnaiger 2014 MitoPathways
Biochemical threshold plot for convergent NS (CI&
II-linked; full line, left) and N (CI-linked) pathway flux based on electron gating (dotted line, right). An enzymatic defect of a single step (CIV) exerts no or little effect on N-pathway and NS-pathway flux (horizontal lines) up to a threshold. Beyond the threshold a linear slope is obtained, which is extrapolated to the apparent excess capacity of the single step. The physiological threshold is overestimated for N-pathway flux, which is restricted by electron gating (Gnaiger 2014 MitoPathways
, Fig. 1.6, edited 2016-02-25).