  Because of the outstanding separating capabilities of two-dimensional
electrophoresis for complete proteins, it would be advantageous to be able to
apply it to all types of proteins. Unfortunately, severe solubility problems
hamper the analysis of many classes of proteins, but especially membrane
proteins. These problems arise mainly in the extraction and isoelectric
focusing steps, and solutions are sought to improve protein solubility under
the conditions prevailing during isoelectric focusing. These solutions deal
mainly with chaotropes and new detergents, which are both able to enhance
protein solubility. The input of these compounds in proteomics analysis of
membrane proteins is discussed, as well as future directions.
