Figure 5.

Ca²⁺-dependence of binding activity between tip- and plate-attached PEG/VE-cadherin-Fc at various Ca²⁺ concentrations. All measurements were obtained with an individual experimental set-up with stepwise increase of the Ca²⁺ concentration by fluid exchange. Binding activity is defined as area between the force distance curve and the neutral line. Each point is the average of at least 400 force distance cycles. Note pronounced cooperativity with a Hill coefficient of 5.04 and an apparent K_D = 1.15 10⁻³ M. Addition of antibody to VE-cadherin-Fc at 20 mM Ca²⁺ caused immediate and almost complete inhibition of binding.