Polyacrylamide gels with modified cross-linkages

The retention of low molecular weight proteins during electrophoresis through gradient polyacrylamide gels was improved when a gradient of N,N′,N″-triallyl citric triamide (TACT) was superimposed on the gradient of acrylamide and N,N′-methylenebisacrylamide (MBA). Gels cross-linked only with N,N′-(1,2-dihydroxyethylene)bisacrylamide (DHEBA) are soluble in dilute periodic acid or dilute aqueous solutions of bases. DHEBA cross-linked gradient gels have a smaller pore structure at high acrylamide concentrations and a more open structure at low acrylamide concentrations than gels cross-linked with MBA. Proteins labeled with tritium and carbon-14 were fractionated through DHEBA cross-linked gradient gels and the isotopes measured after solution of the gel with periodic acid. The mild solubilizing conditions enhanced isotope resolution. The characteristics of several cross-linking molecules are discussed and reasons advanced for the superiority of those with acrylamido end groups.