Direct Measurement of Lateral Mobility

Abstract

This chapter will concentrate on fluorescence photobleaching recovery (FBR), also known as fluorescence recovery after photobleaching (FRAP) or fluorescence microphotolysis,1–6 the microscopic technique by which plasma membrane lateral movement can be determined directly. It will deal initially with the basis of fluorescence and the microscopic techniques that enable fluorescence to be visualized and quantified, and then concentrate on lateral mobility measurements themselves in cytosol, and biological and artificial membranes. It will become clear that the lateral movement of molecules in biological membranes is at least two orders of magnitude slower than that in cytosol. Protein lateral mobility is much slower than that of membrane lipids, implying that membrane proteins are normally limited in their movement. The fact that protein movement is restricted means that the lateral diffusion of proteins within the membrane lipid bilayer is rate limiting in terms of signal transduction at the level of the membrane.7,8