beta-catenin is a member of the armadillo repeat family of proteins and has important functions in cellcell adhesion and Wnt signalling. Different protein species of beta-catenin have been shown to exist in the cell and the relative proportions of these species are altered upon stimulation of cells with Wnt-3a (Gottardi and Gumbiner, 2004). In order to determine whether posttranslational modifications (PTMs) of beta-catenin underlie these different protein species, we have used 2DE separation and immunoblotting with an antibody specific for beta-catenin. High-resolution separation of differentially modified species of beta-catenin in 2DE required the addition of ASB-16, a zwitterionic detergent that can solubilise integral membrane proteins. ASB-16 was also necessary for focussing of other armadillo repeat proteins, such as ?-catenin and p120-catenin. 2DE using ASB-16 allowed detection of a previously unreported phosphorylation site in the transcriptionally active form of beta-catenin that binds to GST-Tcf in response to Wnt signalling.