  We report a realization of an associative memory signal/information
processing system based on simple enzyme-catalyzed biochemical reactions.
Optically detected chemical output is always obtained in response to the
triggering input, but the system can also "learn" by association, to later
respond to the second input if it is initially applied in combination with the
triggering input as the "training" step. This second chemical input is not
self-reinforcing in the present system, which therefore can later "unlearn" to
react to the second input if it is applied several times on its own. Such
processing steps realized with (bio)chemical kinetics promise applications of
bio-inspired/memory-involving components in "networked" (concatenated)
biomolecular processes for multi-signal sensing and complex information
processing.
