Simple models of threshold curves in the expression of inborn errors of metabolism: Application to some experimental observations

The expression of an enzymatic deficiency in a metabolic network can presen t a biochemical threshold. This threshold can be characterised thus: (1) a low activity of the enzyme can sustain a normal flux, but (2) a minute furt her decrease of its activity makes the flux collapse. We give simple mathem atical models displaying such a behaviour, and we apply the models to some examples of oxidative phosphorylation dependency on respiratory chain compl ex deficiency. Copyright (C) 2000 S. Karger AG. Basel.