Electrophoresis is used to separate complex mixtures of proteins (e.g., from cells, subcellular fractions, column fractions, or immunoprecipitates), to investigate subunit composition, track post-translational modifications, and verify identity and homogeneity of protein samples. It can also serve to purify proteins for use in further applications. In polyacrylamide gel electrophoresis, proteins migrate in response to an electrical field through pores in a polyacrylamide gel matrix; pore size decreases with increasing acrylamide concentration. Nondenaturing or "native" electrophoresis-i.e., electrophoresis in the absence of denaturants such as detergents and urea-is an often-overlooked technique for determining the native size, subunit structure, and optimal separation of a protein. Because mobility depends on the size, shape, and intrinsic charge of the protein, nondenaturing electrophoresis provides a set of separation parameters distinctly different from mainly size-dependent denaturing sodium dodecyl sulfate-polyacrylamide gel electrophoresis and charge-dependent isoelectric focusing. Two protocols are presented below. Continuous PAGE is highly flexible, permitting cationic and anionic electrophoresis over a full range of pH. The discontinuous procedure is limited to proteins negatively charged at neutral pH but provides high resolution for accurate size calibration.
Keywords: electrophoresis; native PAGE; native electrophoresis; polyacrylamide; protein; separation.
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