Inverse-gradient polyacrylamide gel electrophoresis in the presence of sodium dodecylsulfate for better separation of protein samples

We found that the relationship between the molecular mass of a protein and its mobility in polyacrylamide gel electrophoresis in the presence of sodium dodecylsulfate on an inverse-gradient (15-5%) gel is linear on a double logarithmic plot. In contrast, this relationship is not linear for proteins resolved on a standard 10% gel, but is fitted to two straight lines. Both gel types gave a similar slope in resolving proteins smaller than 100 kDa but inverse-gradient (15-5%) gel separated proteins with wider range of molecular mass. On the other hand, the standard 10% gel provided better separation of proteins larger than 100 kDa. These results suggest that the 15-5% inverse-gradient gel is best suited for the separation of proteins smaller than 100 kDa. The advantage of inverse-gradient gel SDS-PAGE may stem from the fact that unstacking of SDS-protein complexes in inverse-gradient gels is faster and more complete than in standard 10% gels.