title: Neutral proteases and cathepsin D in human articular cartilage.
abstract: Proteolytic enzymes have been studied in extracts of human articular cartilage by the use of micromethods. The digestion of hemoglobin at pH 3.2 and of cartilage proteoglycan at pH 5 was shown to be due chiefly to cathepsin D. Cathepsin D was purified 900-fold from human patellar cartilage. Its identity was established by its specific cleavage of the B chain of insulin. At least six multiple forms of cathepsin D are present in cartilage; these corresponded to bovine forms 4-9. Cathepsin D had no action on proteins at pH 7.4. However, cartilage extracts digested proteoglycan, casein, and histone at this pH. The proteolytic activities against these three substrates were purified about 170-, 160-, and 70-fold, respectively. Each activity appeared in multiple forms on DEAE-Sephadex chromatography. The three activities appear to be different since cysteine inhibited casein digestion, aurothiomalate inhibited histone digestion, and neither inhibited proteoglycan digestion. Tests with a wide range of inhibitors and activators suggest that these three activities differ from other neutral proteases described in the literature.
mesh_terms: D000368:Aged; D000818:Animals; D001344:Autopsy; D002358:Cartilage, Articular / Q000201:enzymology*; D002364:Caseins / Q000378:metabolism; D002403:Cathepsins / Q000032:analysis*; D002417:Cattle; D002850:Chromatography, Gel; D002852:Chromatography, Ion Exchange; D003545:Cysteine / Q000494:pharmacology; D004591:Electrophoresis, Polyacrylamide Gel; D006025:Glycosaminoglycans / Q000378:metabolism; D006046:Gold / Q000494:pharmacology; D006454:Hemoglobins / Q000378:metabolism; D006657:Histones / Q000378:metabolism; D006801:Humans; D006863:Hydrogen-Ion Concentration; D008293:Malates / Q000494:pharmacology; D008297:Male; D008832:Microchemistry; D008875:Middle Aged; D010329:Patella / Q000201:enzymology; D010447:Peptide Hydrolases / Q000032:analysis* / Q000302:isolation & purification
chemical_list: D002364:Caseins; D006025:Glycosaminoglycans; D006454:Hemoglobins; D006657:Histones; D008293:Malates; D006046:Gold; D002403:Cathepsins; D010447:Peptide Hydrolases; D003545:Cysteine