MMP1（Sang et al.1995），MMP2（Fridman等，1995），MMP3（Goldberg等人1992，Ogata等，1992，Okada等，1992），MMP7（Imai等，1995，Sang等人。1995年), 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).