Observations on Molecular Weight Determinations on Polyacrylamide Gel

Abstract 1. A simple internal calibration technique was used to construct accurate molecular weight-mobility profiles on polyacrylamide gels with well characterized proteins, and the existence of a critical point was observed for small polypeptides. The useful size range limits were determined for several gel concentrations. Apparent molecular weights generally fell within 5 to 6% of literature values, although a few anomalous proteins, notably ribonuclease, considerably exceeded this margin of error. 2. The effects of intrinsic molecular charge and conformation on electrophoretic behavior in the presence of sodium dodecyl sulfate, evaluated by studies on a set of model proteins, were found to be small. 3. The results are in accord with a model in which the protein somehow organizes the sodium dodecyl sulfate anions into a micellar complex of definite size. Although the stoichiometry of the complex is apparently governed not only by the size of the molecule, but also by its state of foldedness, the interplay of anion binding and frictional resistance to passage through the gel is such as to produce a relatively constant log size to mobility ratio. 4. The apparent molecular weights of the five polypeptide chains of Mouse-Elberfeld virus were determined.