A large family of membrane channel proteins selective for transport of water (aquaporins) or water plus glycerol (aquaglyceroporins) has been found in diverse life forms. E. coli has two members of this family¿a water channel, AqpZ, and a glycerol facilitator, GlpF. The crystal structure of GlpF is been solved, and the peptide shows a membrane spanning bundle of 6 alpha helices surrounding an aqueous pore, with a large, extracellular domain, which in the crustal structure is extended, and is approximately 50% the length of the membrane spanning helix bundle. However, it is not clear as to whether the extracelluar domain is also extended in the membrane environment. In this experiment, using contrast matching of membrane and protein, we will compare the relative size of protein and thickness of the bilayer, and investigate whether the extracellular domain indeed extends from the membrane.