Integral membrane protein movement and distribution

Various proteins are free to take a move laterally in the plane of the bilayer. One experiment used to show this included fusing cultured mouse cells with human cells under appropriate conditions to form a hybrid cell which is called as a heterokaryon. A mouse cells were labeled with the mouse protein-specific  antibodies to that  the  green-fiuorescing  dye  fiuorescein   had  been  covalently   attached, similarly  the  human  cells  were  labeled  with  the  red-fiuorescing  dye  rhodamine. Upon cell fusion, the human and mouse proteins as seen under the fiuorescence 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 since they interact with the cytoskeleton inside the cell.

The distribution   of proteins   in membranes   can be revealed   through electron microscopy using the freeze–fracture methods.  In this  method,  a membrane  specimen  is  rapidly  frozen  to  the  temperature  of  liquid  nitrogen

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

–196°C and then fractured through a sharp blow. The bilayer frequently splits into mono- layers, revealing the interior. The exposed surface is then coated with a film of shadowed and carbon with platinum in order for the surface to be viewed in the electron microscope. The fractured surface of the membrane is revealed to have numerous randomly spread protuberances which correspond to integral membrane proteins.