Methodologic problems encountered in the assay of proteinases in Lewis lung carcinoma, a mouse metastasizing tumor

The proteolytic activity in homogenates and extracts of subcellular fractions prepared from subcutaneous Lewis lung carcinoma was determined using proteins and synthetic peptides as substrates. The presence of cathepsin D, plasminogen activator, cathepsin B-, cathepsin G- and elastase-like enzymes was observed. No difference was revealed between the proteolytic activity in homogenates of Lewis lung carcinoma, at the growth stage examined, and in homogenates of normal lung. High specific activities were found in the lysosomal extract, whereas decreasing activities were found in the nuclear extract, the homogenate and the postlysosomal mitochondrial supernatant; no active or trypsin-activatable collagenase activity was detected. The presence in the tumor tissue of these enzymatic activities is in agreement with their proposed role in the process of metastasis. The lack of differences between homogenates of tumor and normal lung tissue suggests that the use of whole cells is required to selectively study tumor proteinases specifically involved in tumor malignancy.