Purification of cathepsin D from cartilage and uterus and its action on the protein-polysaccharide complex of cartilage.

Cathepsin D has been purified approximately 900-fold from two types of cartilage: elastic cartilage of young rabbit ears and hyaline cartilage from the legs of 12to 13-day-old chick embryos. Cathepsin D accounts for most of the hemoglobin-digesting activity of chick cartilage; rabbit ear cartilage also contains a sulfhydryl-dependent acid cathepsin. The identification of the acid proteolytic activity of the cartilages as cathepsin D is based on the specificity of cleavage of the B chain of insulin. The molecular weight of the two enzymes, as estimated by molecular sieving, is about 40,000 to 43,000. The two cartilage enzymes and cathepsin D from bovine uterus all digested the protein-polysaccharide complex of bovine nasal cartilage at pH 5. The digestion could be followed viscosimetrically and it obeyed a second order kinetic expression. The protein-polysaccharide complex was completely degraded to fragments that were larger than single chains of chondroitin sulfate. Digestion at pH 5 was inhibited by e-aminocaproate and arginine (0.1 M), chloroquine and 3-indolepyruvate (0.02 M), and pepstatin (2 X