after some research it still remains unclear to me, how a mass-dependent separation of proteins is possible, if using SDS-PAGE. I have read, that one molecule SDS binds to a protein every two aminoacids. That would not provide a charge proportional to mass, as different aminoacids have different molecular weights. Often it is said, that SDS binds in a ratio of 1,4 g SDS / 1 g protein. That would garantuee a charge in proportion to the weight of the protein. But how is that accomplished by the SDS molecule? And how is that possible, if SDS binds to a protein every two AA? And what does that mean for phosphorylated proteins? They should be heavier, but is that even recognized in the amount of negative charges attached by SDS?
Thank you for answers!
PS: apologies for my english