title: A latent form of cathepsin B in pleural effusions. I. Characterization of the enzyme in breast cancer patients.
abstract: A latent cysteine proteinase has been found in the pleural effusion fluid of patients with breast cancer. It can be converted by pepsin to an active form, the properties of which, including the pH optimum, pH stability, substrate specificity, and sensitivity to various proteinase inhibitors, were found to be closely related to those of cathepsin B. Unlike the pepsin-generated enzyme, which was rapidly inactivated above pH 7.0, the latent enzyme showed substantially higher stability in the region around and above neutral pH. The apparent Mr values of the latent and pepsin-generated enzyme forms were approximately 45,000 and 32,000, respectively. Both enzyme forms exhibited heterogeneous binding affinity to concanavalin A-Sepharose 4B. Altogether, our results demonstrate that a latent cathepsin B form occurs in vivo in pleural effusions of breast cancer patients.
mesh_terms: D001943:Breast Neoplasms / Q000201:enzymology*; D002401:Cathepsin B / Q000032:analysis* / Q000037:antagonists & inhibitors; D004229:Dithiothreitol / Q000494:pharmacology; D004492:Edetic Acid / Q000494:pharmacology; D004789:Enzyme Activation; D005260:Female; D006801:Humans; D006863:Hydrogen-Ion Concentration; D008970:Molecular Weight; D010996:Pleural Effusion / Q000201:enzymology*; D013379:Substrate Specificity
chemical_list: D004492:Edetic Acid; D002401:Cathepsin B; D004229:Dithiothreitol