Protease activities have been recognised as important elements in controlling the composition of the extracellular matrix. Regulated remodelling of the matrix is required for a number of physiological processes including embryonic development. Excessive and unregulated remodelling has been associated with a number of pathological conditions including the metastatic phenotype of malignant cancer (Kim et al., 1998). We have begun a search for protease activities which utilise components of the sea urchin extracellular matrix as substrates. We have identified and purified a 41 kDa protease which is present in the sea urchin egg and embryo. This species possesses a non-specific gelatin-cleavage activity as well as a collagen cleavage activity which appears to be specific for echinoderm collagen (Mayne & Robinson, 1996, 1999).

The 41 kDa collagenase/ gelatinase was inhibited by EGTA and reactivated by calcium. The calcium-concentration dependence for reactivation indicated an apparent kd of 3.7 mM and was coincident with the binding of 80 moles calcium/mole of protein. These results are interpretable in terms of the high concentration of calcium (10 mM) present in seawater. In addition to calcium, seawater also contains 50 mM magnesium. The substantial amounts of calcium bound to the 41 kDa protease suggest the existence of binding sites with both low affinity and specificity for binding metal ions. To determine whether high concentrations of magnesium could influence the interaction of calcium with the 41 kDa species we used both qualitative and quantitative gelatin-cleavage assays to examine protease activity in the presence of both calcium and magnesium.