Matrix Metalloproteinase 28, also known as epilysin, was first cloned from human skin keratinocytes and described to reflect its role in the remodeling of the epidermis. It was found in testis, as well as heart, brain, placenta, lung, prostate, intestine, and colon. MMP28 was later cloned from human lung and found in lung, kidney, brain, skeletal muscle, and several tumor cell lines. At least three MMP28 transcripts of 2.6, 2.0, and 1.2 kb have been reported possibly representing alternatively spliced forms of MMP28. There are two human sequences (isoform1 and isoform 2) which encode proteins of 520 and 393 amino acids with predicted masses of 58.9 and 44.5 kDa respectively. The mouse sequence contains two inserts of 41 and 39 amino acids respectively, relative to the human sequence. Mouse epilysin has a predicted molecular mass of approx. 70 kDa. Mouse and human epilysin are highly conserved and share 97% identical residues. Epilysin (MMP-28) contains the key domains of the other MMPs: a signal peptide, conserved cysteine-containing prodomain (with a furin cleavage site), conserved histidine-containing catalytic domain, hinge domain, and hemopexin domain. MMP28 has a furin cleavage site, similar to MMP11, and is cleaved by the prohormone convertase family of enzymes. Sequence identity between MMP28 and the other MMPs is low overall. MMP28 is most closely related to MMP19 (39% sequence identity). Recombinant MMP28 degrades casein.