Type I collagen is the most abundant structural protein of connective tissues such as skin, bone and tendon. It is synthesized as a procollagen molecule which is characterized by a 300nm triple helical domain flanked by globular N- and C-terminal propeptides. The triple helical domain contains Gly-Xaa-Yaa triplets where Xaa and Yaa are frequently proline and hydroxyproline, respectively. The non-helical propeptides are removed by procollagen N- and C-proteinase activities so that the mature triple helices can self-assemble into collagen fibrils that provide tensile strength to tissues. Type I collagen is a heterotrimer that consists of two alpha1(I) chains and one alpha2(I) chain, although homotrimers consisting of three identical alpha1 (I) chains have also been described. This recombinant mini pro-alpha1(I) collagen is a homotrimer of three shortened alpha1(I) chains with following domain structure from N-to C-terminus: N-propeptide, N-telopeptide, the 33 most N-terminal Gly-Xaa-Yaa repeats, the 33 most C-terminal Gly-Xaa-Yaa repeats, C-telopeptide and C-propeptide. The preparation contains a mixture of the full-length molecule, pN collagen I(alpha1) and the C-terminal propeptide. This truncated pro-alpha1(I) collagen is a substrate for procollagen N-proteinase and procollagen C-proteinase.