  The first realization of a designed, rather than natural, biochemical filter
process is reported and analyzed as a promising network component for
increasing the complexity of biomolecular logic systems. Key challenge in
biochemical logic research has been achieving scalability for complex network
designs. Various logic gates have been realized, but a "toolbox" of analog
elements for interconnectivity and signal processing has remained elusive.
Filters are important as network elements that allow control of noise in signal
transmission and conversion. We report a versatile biochemical filtering
mechanism designed to have sigmoidal response in combination with
signal-conversion process. Horseradish peroxidase-catalyzed oxidation of
chromogenic electron donor by hydrogen peroxide, was altered by adding
ascorbate, allowing to selectively suppress the output signal, modifying the
response from convex to sigmoidal. A kinetic model was developed for evaluation
of the quality of filtering. The results offer improved capabilities for design
of scalable biomolecular information processing systems.

Biological Physics;Soft Condensed Matter;Other Computer Science;Chemical Physics;Molecular Networks