Figure 3.

The initial, slow phase of RI₃₃₂ degradation is omitted in the presence of castanospermine. HeLa-RI₃₃₂ cells were kept untreated (A) or preincubated with castanospermine (CST; 1 mM) (B). All cell cultures were pulse labeled for 10 min and chased for up to 90 min in complete medium in the continued absence or presence of the drug. Cells were lysed, and RI₃₃₂ and ribophorin I were immunoprecipitated and analyzed by SDS-PAGE and fluorography. (C) Quantitations of the bands corresponding to radiolabeled ribophorin I (RI) and RI₃₃₂ to establish the degradation kinetics of RI₃₃₂ in the absence (▵) or presence (□) of castanospermine were performed as described in the legend of Figure 2C and in MATERIALS AND METHODS. Data from six independent experiments are shown.