THE DETECTION, QUANTIFICATION AND PARTIAL CHARACTERIZATION OF CATHEPSIN B-LIKE ACTIVITY IN HUMAN PATHOLOGICAL SYNOVIAL-FLUIDS

In this study, the levels of the cysteine proteinase - cathepsin B wer e measured in diseased synovial fluids using a steady state fluorometr ic assay. Cathepsin B-like activity was shown to be present in all the samples analysed, with the rheumatoid arthritic synovial fluids posse ssing significantly higher concentrations (mean value ca. 416 mg/1) th an the osteoarthritic fluids (mean value ca. 142.4 mg/1). In addition, upon treatment with pepsin, all of the rheumatoid arthritis samples w ere shown to possess additional cathepsin B-like activity, suggesting the presence of a reservoir of latent precursor molecules. By utilisin g a recently developed biotinylated affinity label for cathepsin B-lik e proteinases and sheep anti-(human cathepsin B) antibodies, used in c ombination with SDS-PAGE and Western blotting, the rheumatoid arthriti c synovial cathepsin B was shown to exist in two forms with apparent m olecular masses of M(r) 29 000 and 42 000. We propose that the former is a functionally active proteinase, whereas the latter is a pepsin ac tivatable proform which, when cleaved by this aspartyl proteinase, is converted into a catalytically competent species of M(r) 20 000.