Casein zymograms of culture supernatants after a three day-incubation of meniscal explants under the influence of TNFα, TIMP-3, L-NMMA, or APMA. There are samples from two independent experiments (2 lanes/group) in the upper two zymograms. There is only one major band visible at about 57 kDa (typical size of MMP-3 pro-form ) with lower intensity in control cultures and stronger intensity in TNFα-treated samples. TIMP-3 and L-NMMA have no influence on band intensities. The MMP activator APMA (see lower zymogram) reduces the molecular size of the band (45 kDa) and indicates that the enzyme is pre-dominantly expressed as a pro-form. APMA = p-aminophenyl mercuric acetate; L-NMMA = NG-monomethyl-L-arginine.monoacetate; MMP = matrix metalloproteinase; TIMP = tissue inhibitor of metalloproteinases.