Non-Steady-States, Including Oscillations

In general, a reaction such as Ej will respond faster to a change of flux if the change in the concentration of B (i.e., the required increase in pool size of B) is small. It can be appreciated that, if the extra molecules of B (produced by stimulation of Ej) have to distribute themselves in a large pool (by diffusion) then, for a given change in flux, it will take longer to produce the required increase in the concentration of B and hence E2. 

However, there are occasions when it is necessary to slow down (buffer) a change in concentration for example the decrease in the concentration of ATP during a rapid burst of muscular activity. This can be achieved by increasing the effective pool size of the intermediate by means of an equilibrium, e.g. 

Concentration of X increases from X, to Xf for a time At and then decreases to X again to give a pulsed stimulus (shaded region of graph). Bfis the final steady-state concentration of B, i.e., the concentration that would be reached if the stimulus remained fixed at Xf. For other details see text. 

Oscillations of an intermediate about its steady-state value. For details see text. Two additional points should be noted. First, an observed metabolic oscillation is unlikely to be a pure sine wave, because of the complexity of the regulatory system in situ see Hess (20)]. Second, the sensitivities and rates of cycling and hence the delay are likely to vary with [B] and [Z] this produces a variable amplitude, commonly decreasing with time to give a damped oscillatory response. 

Such oscillations can also occur even if Ea is not saturated with B. In this situation the relative sensitivities of the direct (s ) and the indirect (s s ) routes for stimulation of Ea by B determine whether oscillations occur if s oscillations are possible. Therefore, the existence of 

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