MMP1 (Sang et al. 1995), MMP2 (Fridman et al. 1995), MMP3 (Goldberg et al. 1992, Ogata et al. 1992, Okada et al. 1992), MMP7 (Imai et al. 1995, Sang et al. 1995), MMP10 (Nakamura et al. 1998) and MMP13 (Knauper et al. 1997) activate MMP9 by a stepwise mechanism but the second cleavage is apparently not an autocatalytic event as is the case for MMP1 (Okada et al. 1992). The first site is the Glu59-Met60 bond, generating an inactive 85-86 kDa intermediate (O'Connell et al. 1994), followed by cleavage of the Arg106-Phe107 peptide bond producing the fullly active 82 kDa form of MMP9 (Okada et al. 1992, Fridman et al. 1995).