The data were fit to equation ( ), yielding a concentration of AbHisZ at the inflection point (K0.5) and a Hill coefficient (h) of 8.1  0.4 M and 1.68  0.08, respectively. Nonetheless, this fit is intended only to highlight the sigmoidal behaviour of the data, since the experiment could not be carried out under pseudo-first-order conditions, i. e. [R56A-PaHisGS] ~