Reconstitution of Membrane Transporters

An important goal for a biochemist studying a membrane transporter is to characterize various aspects of its transport function. Initial studies are often carried out in intact cells, but further work is often directed toward studying the functional properties of the purified protein. Some functions of transport proteins may be studied in detergent solution; for example, if the transporter is driven by ATP hydrolysis, the ATPase catalytic activity may be measured in the absence of actual transport, usually by adding the substrate in the presence of ATP and Mg2+ . However, study of the transport process itself can only be carried out in the presence of an impermeable membrane barrier, which necessitates that the transport protein be inserted into a lipid bilayer membrane, a process known as reconstitution. Retention of transport function of the protein is obviously highly desirable, and most reconstitution protocols are designed with this goal in mind. For a detailed discussion of the theory and practice of membrane protein reconstitution, the reader is referred to an excellent review (1 ).