Abstract
A review of continuing studies on the physiological and pathological roles of the lysosomal proteinases, cathepsin D and cathepsin B is presented. Intracellular release of cathepsin D from lysosomes has been demonstrated during myocardial ischemia. Both this proteinase and cathepsin B have been found, by organ culture in the presence of the appropriate antiserum, to be released into the extracellular space in rheumatoid synovium, where they may play a part in cartilage destruction. Also reviewed is the finding of a cathepsin B-like proteinase that, in organ culture, is secreted in markedly increased amounts from human malignant breast carcinomas in comparison to amounts secreted from benign tumors or normal tissue.