Integral membrane proteins
Integral membrane proteins are so designated because they are both structurally and functionally an integral component of a membrane.
Structurally, regions of integral membrane proteins penetrate the hydrophobic regions of the phospholipid bilayer. Because of this interaction, integral membrane proteins can usually only be removed from the membrane by the use of detergents that disrupt the hydrophobic interactions of the bilayer.
Functionally, the presence of these proteins imparts to the membrane specific functions.
In the example below the relationship of the bacterial phototraping pigment, bacteriorhodopsin, and the phospholipid bilayer is illustrated. In this case the integral membrane protein spans the phospholipid bilayer seven times. The part of the protein that is embedded in the hydrophobic regions of the bilayer are alpha helical and composed of predominantly hydrophobic amino acids. The amino terminal end of the protein is in the cytosol while the C terminal region is in the outside of the cell. When a membrane contain this protein the membrane can function in photosynthesis.
Other examples of integral membrane proteins
Na+ - K+ ATPase
ion channels and gates
certain enzymes of the electron transport chains
gap junction proteins