High resolution of proteins by double-inverted gradient polyacrylamide gel electrophoresis (DG-PAGE).

We have designed a new method for high resolution electrophoretic separation of proteins that have similar molecular weights. The proteins migrate first through a conventional gradient gel, in which molecular friction increases as pore size decreases. The proteins then enter an inverted sodium dodecyl sulfate (SDS) gradient gel in which friction decreases; thus, smaller molecules gradually migrate faster and achieve improved separation from larger molecules, which remain near the border between the two gels. We therefore call this technique double-inverted gradient polyacrylamide gel electrophoresis (DG-PAGE). This technique was used to resolve mixtures of aldolase, horseradish peroxidase precursors, glucose 6-phosphate dehydrogenase and pyruvate kinase. By comparison with other established methods, we show that DG-PAGE has a higher resolving power, which achieves clear separation of proteins differing as little as 0.5 kDa in molecular weight.