Processing of wild-type and double-mutant procathepsin G in RBL cells. (A) RBL/CatG and (B) RBL/CatG/Gly₂₀₁/▵Gly₁₉Glu₂₀ cells were pulse-labeled with³⁵S-methionine/³⁵S-cysteine for 30 minutes followed by chase of the label for up to 4 hours. At indicated points, 20 × 10⁶ cells were withdrawn and subjected to solubilization and immunoprecipitation with polyclonal anti-cathepsin G antiserum. In addition, cathepsin G was immunoprecipitated from the incubation medium after each period of chase. The immunoprecipitates were run in SDS-PAGE in a 10% to 20% and a 5% to 20% gradient gel, respectively, whereupon fluorography was performed. The fluorograms were exposed for 6 days and 2 weeks, respectively. The different processing forms of cathepsin G are indicated with arrows to the right. Numbers to the left in this and subsequent figures are the molecular weight values of molecular weight standards.