Pepsin fragments of human placental basement-membrane collagens showing interrupted triple-helical amino acid sequences.

The pepsin digestion of human placental type IV collagen was studied in order to gain insight into the relationships between the fragments alpha 1(IV)95 000 and alpha 2(IV)70 000 which have previously been described. (For nomenclature see Crouch, E., Sage, H. & Bornstein, P. (1980) Proc. Natl. Acad. Sci. U.S.A. 77, 745-749.) Seven smaller pepsin fragments with apparent molecular weights in the range of Mr = 5 000 to 50 000 were also isolated and characterized. The amino-terminal amino acid sequences of alpha 1 (IV)95 000, alpha 2(IV) 70 000 and the smaller pepsin fragments are presented. Kinetic data on the pepsin solubilization provided evidence for the presence of at least two different collagen triple helices within basement membranes and sequence data demonstrated the presence of a number of short non-collagen-like sequences which interrupt the triple helical regions of the alpha chains.