Fig. 1. Effects of tunicamycin and monensin on cathepsin B biosynthesis in SCC-VII cells. Confluent monolayers of SCC-VII cells were metabolically labeled for 1 hour with 100 µCi/ml [³⁵S]methionine and subsequently chased for 4 hours in the absence (-) or continuous presence (+) of 10 µg/ml tunicamycin (A) or 1 µM monensin (B). Cathepsin B was then immunoprecipitated from equivalent amounts of cell and medium extracts and analyzed by SDS-PAGE and fluorography. proCB, procathepsin B; proCB(3), fully glycosylated procathepsin B carrying 3 N-linked oligosaccharide side chains; proCB(0), unglycosylated procathepsin B; scCB, mature cathepsin B (single-chain form). Experiments using cathepsin-B-specific murine embryonic fibroblasts (MEFs) revealed that the band labeled with an asterisk represents a polypeptide unrelated to cathepsin B, which is sometimes nonspecifically co-precipitated from cell extracts by the antiserum used in these studies. Note that this polypeptide is not present in cathepsin B immunoprecipitates from culture media. The migration positions of ¹⁴C-labeled molecular mass standards are indicated.