  We present a generic analytical scheme for the quantification of fluctuations
due to bifunctionality-induced signal transduction within the members of
bacterial two-component system. The proposed model takes into account
post-translational modifications in terms of elementary phosphotransfer
kinetics. Sources of fluctuations due to autophosphorylation, kinase and
phosphatase activity of the sensor kinase have been considered in the model via
Langevin equations, which are then solved within the framework of linear noise
approximation. The resultant analytical expression of phosphorylated response
regulators are then used to quantify the noise profile of biologically
motivated single and branched pathways. Enhancement and reduction of noise in
terms of extra phosphate outflux and influx, respectively, have been analyzed
for the branched system. Furthermore, role of fluctuations of the network
output in the regulation of a promoter with random activation/deactivation
dynamics has been analyzed.
