  In the chemotactic motion of Escherichia coli, the switching of transmembrane
chemoreceptors between active and inactive states is one of the most important
steps of the signaling pathway. We study the effect of this switching
time-scale on the chemotactic performance of the cell. We quantify performance
by the chemotactic drift velocity of the cell. Our extensive numerical
simulations on a detailed theoretical model show that as the activity switching
rate increases, the drift velocity increases and then saturates. Our data also
show the mean duration of a downhill run decreases strongly with the switching
rate, while that of an uphill run decreases relatively slowly. We explain this
effect from temporal variation of activity along uphill and downhill
trajectories. We show that for large and small switching rates the nature of
activity variation show qualitatively different behaviors along a downhill run
but similar behavior along an uphill run. This results in a stronger dependence
of downhill run duration on the switching rate and relatively milder dependence
for uphill run duration.
