Accuracy Assessment for Equilibrium Dissociation Constant Using a Single Binding Isotherm

The equilibrium dissociation constant (Kd) characterizes stability of non-covalent molecular complexes. Determining Kd for highly stable complexes may be extremely inaccurate if the ratio between the concentration of the limiting component (L0) and the a priori unknown value of Kd exceeds an unknown threshold value (aka threshold ratio). The only known approach to reveal this kind of inaccuracy in Kd requires building multiple experimental binding isotherms; it is resource intensive and, therefore, used very rarely. Here we introduce a single-isotherm approach for assessing Kd accuracy via determining the value of L0/Kd, estimating the threshold ratio, and comparing L0/Kd to the threshold ratio. In this proof-of-concept work, we present the theoretical basis and develop a step-by-step algorithm for our single-isotherm approach. We also demonstrate the experimental use of the developed algorithm.