<Li> beta barrel proteins, which are found only in outer membranes of Gram - negative bacteria, and outer membranes of mitochondria and chloroplasts . </Li> <Li> Bitopic proteins are transmembrane proteins that span across the membrane only once . </Li> <Li> Integral monotopic proteins are integral membrane proteins that are attached to only one side of the membrane and do not span the whole way across . </Li> <P> Peripheral membrane proteins are temporarily attached either to the lipid bilayer or to integral proteins by a combination of hydrophobic, electrostatic, and other non-covalent interactions . Peripheral proteins dissociate following treatment with a polar reagent, such as a solution with an elevated pH or high salt concentrations . </P>

Which is not a major function of proteins in the cell membrane