The protein titration needs to span ~5 orders of
magnitude for the specific reason of obtaining good estimates of the limits
L and U.
at low concentrations, fractional protection approaches
a lower limit L
at high concentrations, fractional protection approaches
an upper limit U
the linear relationship P = (U-L)*Y + L is
used to convert fractional protection (which runs from L to U) to fractional
occupancy (Y, which runs from 0 to 1).
It is the fractional occupancy isotherm (ie, data that is bounded by 0 and 1) that we usually see reported, as this form of the data allows comparison between different experiments and testing goodness of fit to modeled curves.