
Negative feedback systems 145
∫
k
r
CheR
T
f
E
(·,·)
Γ′
+
z
·
z
-
+
+
Γ-Γ′
L
E
FIGURE 4.18: Block diagram representation of the methyla-
tion/demethylation mechanism, assuming that CheB
P
can demethylate
also nonactive receptors.
4.6.3 Perfect adaptation requires demethylation of active only
receptors
In [1 2], it was rec ognised that the key assumption required in this model to
obtain perfect adaptation is that CheB
P
can demethylate only active recep-
tors. Although it has not been possible to directly confirm this assumption
experimentally, some supporting evidence for it may be found in the litera-
ture. For instance, in the fa c e of a sudden increase of chemoattractant ...