Description:
<jats:title>Abstract</jats:title><jats:p><jats:italic>The kinetics of annexin A1 binding to solid‐supported lipid bilayers consisting of 1‐palmitoyl‐2‐oleoyl‐</jats:italic>sn<jats:italic>‐glycero‐3‐phosphocholine (POPC)/1‐palmitoyl‐2‐oleoyl‐</jats:italic>sn<jats:italic>‐glycero‐3‐phosphoserine (POPS; 4:1) has been investigated as a function of the calcium ion concentration in the bulk phase. Quartz crystal microbalance measurements in conjunction with scanning force microscopy, fluorescence microscopy, and computer simulations indicate that at a given Ca</jats:italic><jats:sup><jats:italic>2+</jats:italic></jats:sup> <jats:italic>concentration annexin A1 adsorbs irreversibly on membrane domains enriched in POPS. By contrast, annexin A1 adsorbs reversibly on the POPC‐enriched phase, which is composed of single POPS molecules embedded within a POPC matrix. The overall area occupied by the POPS‐enriched phase is controlled by the CaCl<jats:sub>2</jats:sub> concentration. Monte Carlo simulations suggest that the area of the POPS‐enriched phase increases by a factor of 7 when the Ca</jats:italic><jats:sup><jats:italic>2+</jats:italic></jats:sup> <jats:italic>concentration is changed from 0.01 to 1 m<jats:sc>M</jats:sc>.</jats:italic></jats:p>