Free-boundary Electrophoresis of Sodium Dodecyl Sulfate-Protein Polypeptide Complexes with Special Reference to SDS-Polyacrylamide Gel Electrophoresis

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Abstract
Free-boundary electrophoresis was carried out with complexes formed between sodium dodecyl sulfate and polypeptides derived from various proteins by cleavage of their disulfide linkages. It was found that the electrophoretic mobilities of the complexes were independent of the molecular weights of the polypeptides in the range 10,000 to 70,000 daltons. It is clear that the apparent electrophoretic mobilities of the polypeptides in SDS-polyacrylamide gel electrophoresis become uniquely dependent on the molecular weights of the polypeptides chiefly due to the molecular sieve effect of the gel matrix. The mobilities of complexes formed between sodium dodecyl sulfate and polyvinylpyrrolidone were also found to be independent of the molecular weight of the polymer. The electrophoretic mobility observed was about −2.6xl0−4cm2−sec−1.volt−1 at 25°C, whether the polymer component of the complex was a protein polypeptide or polyvinylpyrrolidone. A prolate ellipsoid model has been proposed for the complexes formed between sodium dodecyl sulfate and protein polypeptides by Reynolds and Tanford (J. Biol. Chem., 245, 5161 (1970)). An alternative model that is applicable to either of the two kinds of complexes studied was proposed based on the present findings. In the model, the polymer chain is considered to be mostly flexible, and sodium dodecyl sulfate clusters are arranged along the polymer chain.

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