Spread monolayers of proteins.

The study of spread monolayers of proteins is of interest for understanding the fundamental behavior of proteins as well as the many phenomena resulting from their ubiquitous presence at interfaces in nature. Spread monolayers of proteins is a branch of the developing field of membrane mimetic chemistry. In recent times, it has been somewhat neglected in comparison to other branches (such as bilayers, liposomes and vesicles), despite the unique advantage that the arrangement and packing of molecules in monolayers may be measured and controlled. Methods for spreading proteins and techniques used for their manipulation are outlined. As well as the more traditional methods (such as surface pressure, potential and viscosity), more recent innovations, including removal of monolayers on slides for study by radiotracer techniques, electron diffraction and infrared (IR) spectroscopy, are discussed. Direct optical methods for the study of monolayers in situ are also available (e.g., multiple reflectance spectroscopy, ellipsometry). The use of measurements in the low pressure region to measure molecular weights is discussed. At higher pressures, configurational changes, surface coagulation and desorption are all observed. Experimental and theoretical work on the desorption of proteins from the air/water interface is reviewed. The introduction of multicompartment film balances has proved valuable for the study of reactions occurring in monolayers. This instrumentation has been applied to the study of enzyme reactions at the surface, of direct relevance to reactions where the enzyme is immobilized in the cell membrane. Some applications of monolayer studies are briefly illustrated with reference to biological membranes, foams and emulsions and biomedical problems.