Sodium dodecyl sulfate-protein polypeptide complexes in 8 M urea with special reference to sodium dodecyl sulfate-polyacrylamide gel electrophoresis.

The effects of 8 M urea on the complexes formed between sodium dodecyl sulfate and protein polypeptide were found to be as follows: (1) The maximum amount of SDS bound is reduced by almost half, and the minimum equilibrium concentration of SDS necessary to reach saturation was nearly doubled; (2) The apparent content of alpha-helical structure deduced from CD measurement is reduced to only 50--70% of that in the presence of sodium dodecyl sulfate alone; (3) The effective size of the sodium dodecyl sulfate-protein polypeptide complex deduced from viscosity measurements is increased, but is still smaller than the effective size of the protein in 8 M urea alone.