  Multisite protein modification is a ubiquitous mechanism utilized by cells to
control protein functions. We have recently proposed a dynamical description of
multisite protein modification which embodies all the essential features of the
process (E. Milotti, A. Del Fabbro, C. Dalla Pellegrina, and R. Chignola,
Physica A, in press), and we have used this model to analyze the stability and
the time-scales of this mechanism. The same model can be used to understand how
the system responds to stimuli: here we show that it displays
frequency-dependent dynamical hysteresis. This behavior closely parallels --
with the due differences -- what is observed in magnetic systems. By selecting
model parameters that span the known biological ranges, we find that the
frequency-dependent features cover the band of the observed oscillations of
molecular intracellular signals, and this suggests that this mechanism may have
an important role in cellular information processing.
