Cathepsin D activity in bovine articular cartilage, synovial membrane and fluid: degradation of cartilage proteoglycans from same joint.

Cathepsin D type proteases were extracted from articular cartilage, synovial membrane, and synovial fluid from normal, adult bovine knee joints. A sensitive enzyme assay made it possible to measure protease activity in the different tissues from individual joints. Highest activity was found in the synovial membrane, while cell free synovial fluids contained comparatively low activity. The degrading effect on articular cartilage proteoglycans (PGC and PGS), isolated from the same joints, was demonstrated by gelfiltration on Sepharose columns and by viscometry. Gelfiltration profiles of incubation mixtures indicated a proteolytic effect on PGC and on PGS), at pH 3.5, in concentrations of enzyme and proteoglycans found in cartilage tissue. No effect at neutral pH was obtained despite a 100-fold increase of enzyme concentration. These findings were supported by viscometry data. The degrading effect of enzymes from all sources was completely inhibited by pepstatin.