Revised Manuscript Received December 3, 1992 abstract: The degradation of extracellular matrix is an important facet of many physiological and pathological processes. The collagenases form a family of matrix degradative enzymes that have similar active site sequences and activation mechanisms and are inhibited by a specific class of proteinase inhibitors referred to as tissue inhibitors of metalloproteinases. Regulation of enzyme activity is a complex process involving control at multiple levels: message transcription and translation, activation of latent proenzymes, inhibition of activity by specific inhibitors, and degradation of activated enzymes. We have examined the role of the proteinase inhibitor tissue inhibitor of metalloproteinases-2 (TIMP-2) on two of these processes: the autoactivation and autodegradation of the human 72-kDa type IV collagenase. We compared the stability of the enzyme in these two processes using threedifferent enzyme preparations: the enzyme-inhibitor complex as isolated from human A2058 melanoma cells, recombinant enzyme free of TIMP-2, and enzyme separated from TIMP-2 byacid denaturation. We have found little evidence to support the hypothesis that theenzyme is able to autoactivate, as no autoactivation occurs in thepresence of TIMP-2 and only 20% autoactivation occurs in its absence, andthen only after 24 h of incubation at 37 C. However, TIMP-2 does appear to inhibit autodegradation, possibly by a mechanism distinct from its ability to inhibit substrate proteolysis. Enzyme isolated via chromatography involving acid mobile phases produces a mixture of cleavage products that is mostly denatured, inactive enzyme fragments. The role of TIMP-2 as an inhibitor of autodegradation suggests that the enzyme may show two physiological phenotypes: the free enzyme having a high level of activity and rapid autodegradation and enzyme-inhibitor complex having a low level of activity resistant to autodegradation.