Fig. 4. Immunoprecipitation and in vitro phosphorylation of CFTR in IB3-1 cells. (A) Location of band-B and -C forms are shown together with the positions of molecular weight markers. Immunoprecipitation and in vitro phosphorylation of non-mutated CFTR from Calu-3 cells (lane 2) and delF508 from IB3-1 cells treated for 2 hours with 250 µM MPB-91 (+MPB-91, lane 5) or without treatment (–MPB-91, lane 4). Lanes 1 and 3 are control experiments without CFTR antibody. (B) Densitometric measurement of CFTR after in vitro phosphorylation. Percentage of fully processed band C and B are shown after a 2 hour treatment of IB3-1 cells with 250 µM MPB-91 (+MPB-91) or without treatment (–MPB-91).