Moiety Conservation and Flux Enhancement

Abstract

In Chapter 1 Kell and Mendes claim that “the flux of several model pathways responds to the total amount of conserved moiety according to a bell-shaped curve”, substantiating this with simulation results of a simple branched metabolic pathway. Whilst we certainly agree that the total amount of moiety can control the flux through a pathway, we show here that the observed bell-shaped curve is the result of unrealistic model definition and the existence of a second moiety-conserved cycle in the system they simulated. We present alternative models which do not show the bell-shaped dependence of the flux on the total amount of moiety. We disagree strongly with the statement that there is an “optimal amount of cofactor for a given pathway flux” in the sense of a maximum of a bell-shaped response; in fact, experimental evidence shows that enzymes are usually almost saturated with cofactor. We therefore question whether the cell alters total amount of moiety as a regulatory mechanism to change fluxes.