  Experimental and theoretical analyses of the lactate dehydrogenase and
glutathione reductase based enzymatic AND logic gates in which the enzymes and
their substrates serve as logic inputs are performed. These two systems are
examples of the novel, previously unexplored, class of biochemical logic gates
that illustrate potential biomedical applications of biochemical logic. They
are characterized by input concentrations at logic 0 and 1 states corresponding
to normal and abnormal physiological conditions. Our analysis shows that the
logic gates under investigation have similar noise characteristics. Both
significantly amplify random noise present in inputs, however we establish that
for realistic widths of the input noise distributions, it is still possible to
differentiate between the logic 0 and 1 states of the output. This indicates
that reliable detection of abnormal biomedical conditions is indeed possible
with such enzyme-logic systems.
