Antigenic and immunogenic properties of membrane proteins solubilized by sodium desoxycholate, papain digestion or high ionic strength

Comparison between antigens solubilized from MOPC-460 mouse plasmacytoma cell membranes by means of three methods (treatment with a surfactant: sodium desoxycholate (DOC); high ionic strength, using 3 M potassium chloride (3 M KCl); insolubilized papain (PAP) digestion) is reported. DOC displayed the greatest quantitative efficiency and brought more than 80 per cent of the membrane proteins in solution, as well as about 15 per cent of the protein-bound sugars. 3M KCl and papain solubilized 16 per cent and 10 per cent proteins and 3 per cent and 5 per cent sugars respectively. SDS-acrylamide electrophoresis showed that DOC also solubilized the greatest number of proteins and demonstrated the disadvantages associated with PAP digestion. In the rabbit, however, DOC-solubilized proteins displayed poor immunogenicity. In particular, precipitating antibodies against membrane antigens that were not equally solubilized by 3 M KCl could not be obtained. It is deduced from what is known of surfactant mechanisms that DOC solubilizes both 'integral' and 'extrinsic' membrane proteins, whereas the ionic strength acts primarily on the latter. Cross-adsorption experiments with the antisera produced against antigens solubilized with the two agents showed that the great majority of the antibodies induced against antigens solubilized from cell membranes were directed against 'extrinsic' proteins.