Figure 1. Active MMP-2 is present only in human periodontal ligament (PDL) fibroblast cell layers. (A) Immunoblotting of MMP-2, membrane-type matrix metalloproteinases-1 (MT1-MMP), and tissue inhibitor of matrix metalloproteinsase-2 (TIMP-2). Gingival and PDL fibroblasts were cultured for 6 wks. A 10-µg quantity of cell lysate underwent electrophoresis on 10% polyacrylamide gels and was immunoblotted for MMP-2, MT1-MMP, and TIMP-2 analyses. Equivalent protein loading was confirmed by ß-actin. (B) MMP immunoreactivity in biotinylated and intracellular fractions of PDL fibroblasts. PDL fibroblasts were cultured for 6 wks. Cell-surface and extracellular proteins were then biotinylated with non-cell-permeable biotin, and the biotinylated and intracellular fractions were immunoblotted with MMP-2 (upper panel) and actin (lower panel). (C) MMP-2 in the culture media. Serum-free culture media were collected from gingival and PDL fibroblasts at 6 wks. The harvested media (10 µg) were subjected to gelatin zymography.