FIGURE 9.

Selective extraction of collagen type III from human articular cartilage by MMP3. a, minced cartilage after 4 m guanidine HCl extraction was serially extracted twice for 24 h with recombinant MMP3. Replicate aliquots of each extract were run on 10% SDS-PAGE ± DTT, stained directly with Coomassie Blue, or immunoblotted using three different mAbs, 4G9, 2C3, or 1C10, which recognize the α1(III) N-propeptide, α1(III) N-telopeptide proteolytic neoepitope, and α1(II) triple-helical domain, respectively. Bands in the lower half of the Coomassie-stained lanes are from the enzyme preparation. Lane 1, first 24-h extract; lane 2, second 24-h extract. b, another sample of the same cartilage guanidine-HCl residue was digested with pepsin, the digest fractionated into 0.8 m, 1.2 m, and 2.2 m NaCl precipitates, and each run on 6% SDS-PAGE ± DTT. c, proteolytic cleavage sites and molecular features of collagen type III are illustrated.