  We report a study of a system which involves an enzymatic cascade realizing
an AND logic gate, with an added photochemical processing of the output
allowing to make the gate's response sigmoid in both inputs. New functional
forms are developed for quantifying the kinetics of such systems, specifically
designed to model their response in terms of signal and information processing.
These theoretical expressions are tested for the studied system, which also
allows us to consider aspects of biochemical information processing such as
noise transmission properties and control of timing of the chemical and
physical steps.
