... across cellular membranes and into the cytoplasm [3,4]. The first step in the intoxication pro-cess involves DT binding, via its B-subunit domain,to the heparin-binding epidermal growth factor-likegrowth ... containing 6 mm CaCl2, in the presence orabsence of protease inhibitors. To determine the integrityof DT, the proteolytic reaction was stopped by the additionof reducing or nonreducing SDS ... event or intermolecular processing by endo-somal cathepsins or other endosomal endopeptidases.Interestingly, it has been shown that, upon reaching the cell surface or during cycling between the...