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Abstract
Identifying the basic module of enzymatic amplification as an irreversible cycle of
messenger activation/deactivation by a "push-pull" pair of opposing enzymes, we analyze
it in terms of gain, bandwidth, noise, and power consumption. The enzymatic signal
transduction cascade is viewed as an information channel, the design of which is governed
by the statistical properties of the input and the noise and dynamic range constraints
of the output. With the example of vertebrate phototransduction cascade we demonstrate
that all of the relevant engineering parameters are controlled by enzyme concentrations
and, from functional considerations, derive bounds on the required protein numbers.
Conversely, the ability of enzymatic networks to change their response characteristics
by varying only the abundance of different enzymes illustrates how functional diversity
may be built from nearly conserved molecular components.