Extracellular presence of the lysosomal proteinase cathepsin B in rheumatoid synovium and its activity at neutral pH
✍ Scribed by John S. Mort; Anneliese D. Recklies; A. Robin Poole
- Publisher
- John Wiley and Sons
- Year
- 1984
- Tongue
- English
- Weight
- 661 KB
- Volume
- 27
- Category
- Article
- ISSN
- 0004-3591
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✦ Synopsis
The presence of the lysosomal proteinases cathepsin B and cathepsin D at extracellular sites in rheumatoid synovium was demonstrated using the antibody capture technique. Unlike cathepsin D, the cysteine proteinase cathepsin B was commonly detected only at the edges of the synovial explants. Radioimmunoassay and enzyme activity assay of these proteinases demonstrated that both were released from rheumatoid synovi-a1 cells in comparable amounts. Since lysosomal cathepsin B is unstable and denatured at physiologic pH and the antibody used only recognizes inactivated enzyme, we believe the selective detection of cathepsin B at the edge of the synovium may be due to the proteinase maintaining a native conformation within the explant, where the pH may be low enough to permit this. By use of a fluorescent substrate in a sensitive, continuous enzyme assay, cathepsin B was shown to express significant activity at neutral and alkaline pH before being inactivated. This and earlier work from this laboratory indicate that cathepsin B secreted by rheumatoid synovial cells may possess extracellular activity in vivo and be