Figure 1
Theoretical calculation of how increased binding affinity due to depolarization could increase annexin V binding under different conditions of affinity and ligand concentration. Five theoretical binding isotherms were calculated for Kd values of 1, 3, 10, 30, and 100 nM from the Langmuir isotherm (bound fraction = [annexin V]/([annexin V] + Kd)). These curves were then used to calculate the effect of a ten-fold increase in binding affinity (ΔpKd of +1) on the relative amount of annexin V bound to a cell for three different situations: Kd changes from 10 nM to 1 nM (left curve); 30 to 3 nM (middle curve); 100 to 10 nM (right curve). The Kd range from 1 to 100 nM was chosen for illustration because experimental apparent Kd values for annexin V binding to cells are in this general range [19–21]. The vertical bar indicates the experimentally observed range of depolarized/undepolarized binding ratios under the various experimental conditions used in this study (see subsequent figures).