Electrophoresis in gels containing zwitterionic groups

Abstract

AbstractA zwitterionic methacrylamide derivative, (3‐sulfopropyl)dimethy1(3‐methacrylamidopropyl) ammonium inner salt (MAPS), was synthesized and then copolymerized with N,N′‐methylenebisacrylamide (Bis) to make gels carrying covalently bound sulfobetaine groups. Gels were also prepared with the addition of (3‐sulfopropyl)trimethyl ammonium inner salt (TMAPS) to Bis‐crosslinked polyacrylamide prior to polymerization. The properties of these gels in gel electrophoresis and electrofocusing were tested and compared with those of Bis‐crosslinked polyacrylamide.In MAPS gels the absolute migration velocities of proteins and dyes at either polarity of migration were decreased. Anionic species were much more strongly retarded than cationic species. Ferguson plots (based on protein mobilities relative to dye in a continuous buffer) of catalase at pH 4 obtained on MAPS gels had a similar slope but lower y‐intercept compared with those on equivalent polyacrylamide gels, indicating that the available (effective) net charge on the protein was decreased because it interacts with the zwitterionic charge on the gel. Similarly, the addition of TMAPS to polyacrylamide decreased the relative catalase mobility at non‐restrictive gel concentrations. However, at gel concentrations above 4 %T, relative mobilities were increased, presumably because the effective pore size of the gel was increased through inhibition of polymerization by the zwitterionic compound.MAPS gels did not exhibit electroendosmosis by the criterion of cyanocobalamin displacement. Resolution between peptides in MAPS gels, and between proteins in ternary copolymer gels made of MAPS, Bis and polyacrylamide, was similar to that on polyacrylamide. Bands of catalase appeared sharpened in MAPS gels. pH Gradients form, decay and exhibit conductance gaps in MAPS electrofocusing gels and in polyacrylamide gels in presence of 0.25‐1.5 M TMAPS, in a manner which was qualitatively indistinguishable from polyacrylamide.