Digestion of native collagen in the triple helical region at Xaa-|-Gly bonds. With synthetic peptides, a preference is shown for Gly at P3 and P1', Pro and Ala at P2 and P2', and hydroxyproline, Ala or Arg at P3'. Binds 1 zinc ion. Proteolytic cleavage might yield three different active forms. Belongs to the peptidase M9A family.