We have investigated the effect of integral membrane proteins upon the
fracturing of frozen lipid bilayers. This investigation has been part of an
effort to develop freeze fracture labeling techniques and to assess the
possible breakage of covalent protein bonds during the freeze fracture
process. We have developed an experimental protocol utilizing lectin
affinity columns which should detect small amounts of covalent bond breakage
during the fracture of liposomes containing purified (1) glycophorin (a
transmembrane glycoprotein of human erythrocyte membranes). To fracture
liposomes in bulk, frozen liposomes are ground repeatedly under liquid
nitrogen. Failure to detect any significant covalent bond breakage (contrary
to (2)) led us to question the effectiveness of our grinding procedure in
fracturing and splitting lipid bilayers.
