  Living cell signaling systems include multistep biochemical signaling
reaction cascades (BSCs) comprising modifications of molecular signaling
proteins. Substantial data on BSCs have been accumulated in the field of
molecular biology and the analysis of signaling systems requires qualitative
evaluation. However, quantification of the information and channel capacity of
BSCs has not been focused on from the perspective of information theory. In the
current study, we aimed to derive basic equations for describing the channel
capacity and information density of BSCs using the fluctuation theorem. From
the results, channel capacity and information density can be described using
the average entropy production rate when the signaling system is minimally
redundant. The channel capacity could actually be calculated for the
mitogen-activated protein kinase BSC when it was minimally redundant. This
quantitative method of examination is applicable to the quantitative analysis
of BSCs.
