Effect of inhibitors on S1 processing and PT activity in CHO cells. (A, B) CHO cells were preincubated with the indicated inhibitor before addition of PT (20 nM) and then analyzed for S1 processing as before. Western blots are shown with unprocessed and processed (S1p) forms of S1 indicated. Lanes marked C are PT (100–200 ng) loading controls. DMSO = dimethylsulfoxide (solvent control). Metalloprotease inhibitor concentrations are indicated (mM). 0 = no inhibitor. BafA1 = bafilomycin A1. (C) Effect of inhibitors on ADP-ribosylation of CHO cell G proteins by PT. Autoradiogram of cellular ADP-ribosylation assay after treatment of CHO cells with the indicated inhibitor and either PT or PT* (last lane). Radiolabeled band (approximately 41 kDa) corresponds presumably with Giα2 and Giα3 .