Molecular Weight Determination by Electrophoresis of SDS-Denatured Proteins

There is a good reason why it is called apparent molecular weight. SDS-PAGE and Simple Western separate proteins based on the amount of SDS bound to the protein during denaturation. The correlation between motility and molecular weight (MW) is based on the uniform binding of negatively charged SDS to the protein (1.4g SDS/g Protein) which results in a constant charge-mass ratio. In reality, the amount of SDS bound is anything but constant and it's affected by many factors...