Membrane proteins interact with or are part of biological membranes and perform a variety of functions. Receptor proteins (e.g. GPCRs) detect molecules outside the cell and activate internal signal transduction pathways. Transport proteins (e.g., channels/pores, transporters) move molecules and ions across the membrane. Cell adhesion molecules allow cells to adhere and to communicate. A variety of Enzymes such as oxidoreductases, transferases and hydrolases are active at the membrane. Integral membrane proteins often have transmembrane-helix or β-barrel structures and are difficult to study due to their inherent need for lipids as stabilizers of their structure and function. Detergents-solubilization of membrane proteins is often required for their extraction from the membrane. The choice of detergent may be crucial for retaining protein activity. Generally, detergents should be used at a concentration above their critical micelle concentration (CMC). Micelles formed above the CMC can mimic a membrane environment.