The 42 kDa intermediate form of MMP1 is fully activated by cleavage of the Gln99-Phe100 bond, producing a 41 kDa protein. MMP2 (Crabbe et al. 1994), MMP3 (Suzuki et al. 1990, Nagase et al. 1992), MMP7 (Imai et al. 1995), MMP10 (Nicholson et al. 1989) and MMP11 (Murphy et al. 1993) are able to convert the 42 kDa intermediate to fully activated 41 kDa form though they are not able to initiate activation of proMMP1 effectively (Nagase et al. 1992). MMP3 regulates MMP1 collagenase activity in human rheumatoid synovial fibroblasts (Unemori et al. 1991).