Gradient SDS Polyacrylamide Gel Electrophoresis

The preparation of fixed-concentration polyacrylamide gels has been described in Chapter 6. However, the use of polyacrylamide gels that have a gradient of increasing acrylamide concentration (and hence decreasing pore size) can sometimes have advantages over fixed-concentration acrylamide gels. During electrophoresis in gradient gels, proteins migrate until the decreasing pore size impedes further progress. Once the "pore limit" is reached, the protein banding pattern does not change appreciably with time, although migration does not cease completely. There are three main advantages of gradient gels over linear gels: 1.The advancing edge of the migrating protein zone is retarded more than the trailing edge, thus resulting in a sharpening of the protein bands.2.The gradient in pore size increases the range of molecular weights that can be fractionated in a single gel run.3.Proteins with close molecular weight values are more likely to separate in a gradient gel than a linear gel.