Response coefficients of interconvertible enzyme cascades towards effectors that act on one or both modifier enzymes

Explicit expressions have been derived for the response coefficients for the effect of activator and inhibitor concentrations on the fraction in the active state of the target enzyme of a monocyclic interconvertible enzyme cascade. These allow one to assess the adequacy of such a cascade for producing a highly sensitive response to an effector. Numerical studies indicate that this type of system can readily generate response coefficients of about seven, even without requiring both modification reactions to be modulated simultaneously, and without requiring all of the parameters that characterize the system to have their optimum values. Thus, a monocyclic cascade can constitute a highly effective on/off switching device in a linear pathway.