The catalytic domains of two matrix metalloproteinases--collagenase-1 and stromelysin-1 have been studied by means of fluorescence spectroscopy and high hydrostatic pressure. The hydrophobic fluorescence probe ANS could bind to stromelysin-1, with a dissociation constant of 26.3 &mgr;mol/L, but could not bind to collagenase-1, indicating that there exists a hydrophobic site on the surface of stromelysin-1. Further study suggests that the hydrophobic site may not be the catalytic site. The biological activity of catalytic domains of collagenase-1 and stromelysin-1 showed obvious difference under high pressure the activity of collagenase-1 increased with elevating pressure, with an activation volume of D18.9 ml/mol however, the activity of stromelysin-1 did not change under high pressure. The results indicate that there are some obvious differences between the catalytic domain conformations of these two enzymes, though the crystal analysis indicated that they were very similar as reported before.