Fig. 3.

Cooperativity of Ca²⁺-triggered fusion. (A) Shown are the rapid burst magnitude (as defined in Materials and Methods) for the full system (SNAREs, synaptotagmin 1, and complexin) (green) and with all components except complexin (purple) as a function of Ca²⁺ concentration; mean values with error bars (standard deviations) are computed for multiple experiments. (B and C) Mean values of the cooperativity and K_d obtained by fitting a Hill function to the Ca²⁺ titration curves for the full system and the system without complexin (error bars indicate the goodness of the fit).