You are interested in the mobility of two different unknown integral plasma membrane proteinsprotein ...

Answer: For Fluorescence Recovery After Photobleaching (FRAP), the fluorescence of proteins in a spot on the membrane is bleached with a laser beam and recovery of fluorescence in that spot is measured over time. Recovery occurs when the proteins with photobleached labels diffuse out of the spot and proteins with unbleached labels diffuse in. Rapid recovery of protein X fluorescence indicates that protein X readily diffuses in the plasma membrane with little to no constraint. The slower and incomplete recovery of protein Y fluorescence indicates protein Y diffusion is constrained. Protein Y diffusion could be constrained, because the protein is associated associated with other membrane constituents in large complexes or lipid rafts, or it could be associated with extracellular or intracellular peripheral structures such as the extracellular matrix or the cytoskeleton.