CTSB and neoplasm: A 38 kDa intermediate form of the enzyme was present only in lysates of the SUM149 cells and mature double chain cathepsin B was secreted only from SUM190 cells (Figure 1a); these differences between the two cell lines are likely to be due to variations in the extent of processing of the proenzyme into the various mature forms, as we have observed in a variety of human tumor tissues [28].