Figure 5.

Stimulus-dependent release from INS cells treated with tunicamycin. Untreated INS cells (left) or those pretreated with tunicamycin (right) were pulse labeled and chased for 3.5 h before 60-min collections of stimulated (+) or unstimulated (−) secretion, or the resulting cell lysates were analyzed by immunoprecipitation with antiinsulin (A) or anti– cathepsin L (B). For INS cells treated with tunicamycin, samples were intentionally double loaded to enhance the sensitivity of detection of mature cathepsin L forms. Note that after tunicamycin treatment, the amount of intracellular precursor increased disproportionately, as did the amount of stimulus-dependent secretion of ProL. The positions of proinsulin, insulin, presumptive proinsulin conversion intermediates (small bracket), glycosylated and unglycosylated ProL, and bands comprising glycosylated and unglycosylated mature cathepsin L (large brackets) are shown.