Various proteins are free to take a move laterally in the plane of the bilayer. One experiment used to represent this included fusing cultured mouse cells with human cells under appropriate conditions to variety a hybrid cell which is known as a heterokaryon. A mouse cells were labeled with the mouse protein-specific  antibodies to that  the  green-fluorescing  dye  fluorescein   had  been  covalently   attached, similarly  the  human  cells  were  labeled  with  the  red-fluorescing  dye  rhodamine. Upon cell fusion, the human and mouse proteins as seen under the fluorescence microscope were segregated on the two halves of the heterokaryon in figure.  After 37°C in 40 min, moreover, the mouse and human proteins had completely intermingled. Lowering the temperature to follows 15°C inhibited this procedure, denotes in which the proteins are free to diffuse laterally in the membrane and which this movement is slowed as the temperature is lowered.  It should be noted, by, that some integral membrane proteins are not free to move laterally in the membrane as they interact with the cytoskeleton inside the cell.

figure: (a) Movement and (b) distribution (as shown by freeze-fracture electron microscopy) of integral membrane proteins.