A cathepsin D type enzyme was present in 2-3 times greater amount in early osteoarthritic and discolored human articular cartilage than in apparently normal cartilage. This cathepsin D type enzyme was the predominant hemoglobin and proteoglycan digesting protease in the human articular cartilage investigated. This human cathepsin D type enzyme as well as a highly purified cathepsin D preparation from bovine uterus degraded proteoglycan subunit maximally at pH 5. Both enzyme preparations did not digest hemoglobin at pH 6-8, but degraded proteoglycan subunit considerably at neutral pH. The activity of the human cathepsin extract was not affected by reagent that inhibit or activate cathepsin A and B or diisopropylfluorophosphate, but was inhibited by chloroquine at pH 7.0. Although no neutral proteases that digest hemoglobin or are inhibited by diisopropylfluorophosphate were detected in the human cathepsin extract and the highly purified cathepsin D preparation, the remarkable degradative action on proteoglycan subunit at neutral pH suggests that they may also contain a neutral protease that acts on proteoglycan but not hemoglobin.
|Original language||English (US)|
|Number of pages||5|
|State||Published - Dec 1 1973|
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