Structural features of native insoluble and plasmin-solubilized type I collagen as a representative example. Native, insoluble fibrillar type I collagen (from bovine achilles tendon) and pepsin-solubilized type I collagen (from human placenta) were coated on glass coverslips as described in Materials and Methods. Surface replication analysis of insoluble type I collagen (A) showed a characteristic banded pattern that was noticeably absent from the smaller fibrils derived from pepsin-solubilized type I collagen (B), where microfibril assemblies displayed a nonbanded spiraled configuration. Polyacrylamide gel electrophoresis under denaturing and nonreducing conditions showed the presence of the 1(I) and 2(I) type I collagen subunits as well as high molecular weight multimers (right).