Determining the dissociation rate constant for FPR dimer by observing single receptor molecules. (A) The distributions of the duration of each colocalization event for D71A (left) and a monomer reference molecule ACP(DY547)-TM (right), observed at a time resolution of 4 ms. (B) The distribution of photobleaching lifetime for each monomer spot. See the text for details. (C) The distribution of the duration of each colocalization event for D71A, observed at a 33-ms resolution.