Mobility of membrane proteins
Membrane proteins and phospholipids are unable to move back and forth
between the inner and outer leaflets of the membrane at an appreciable
rate. However, because they are inserted into a fluid lipid bilayer, both
proteins and lipids are able to diffuse laterally through the membrane. This
lateral movement was first shown directly in an experiment reported by
Larry Frye and Michael Edidin in 1970, which provided support for the fluid
mosaic model. F and E in their experiment fused human and mouse cells in
culture to produce human-mouse cell hybrids .They then analyzed the
distribution of proteins in the membranes of these hybrid cells using
antibodies that specifically recognize proteins of human and mouse origin.
These antibodies were labeled with different fluorescent dyes, so the
human and mouse proteins could be distinguished by fluorescence
microscopy. Immediately after fusion, human and mouse proteins were
localized to different halves of the hybrid cells. However, after a brief
period of incubation at 37°C, the human and mouse proteins were completely
intermixed over the cell surface, indicating that they moved freely through
the plasma membrane.