Fig. 7. Movement of latex beads coated with the different proteins. (Left traces) X versus Y plots of bead movement in the plane of the membrane. (Right traces) Displacement versus time of beads. At time zero, the beads were placed with the optical trap near the leading edge of the cell and maintained on the cell surface for 4 seconds. The laser was then stopped and the bead released. Unbound beads quickly drifted out of focus while bound beads remained on the cell surface.