CHARACTERIZATION OF PEPSIN FRAGMENTS OF BASEMENT-MEMBRANE COLLAGEN OBTAINED FROM A MOUSE-TUMOR

Basement membrane collagen was purified from an acetic acid extract of a mouse tumor and subjected to pepsin treatment. At initial stages disulfide‐linked molecules, consisting of peptide chains with an apparent molecular weight of 140000, were formed which were some 15–20% smaller than the chains in the original protein. In a second stage further fragmentation occurred producing at least five peptides ranging in molecular weight from 27000 to 72000. Each of these peptides was isolated and characterised by amino acid composition, cyanogen bromide cleavage, circular dichroism and antigenic activity. The data indicate that the major portion of the initial pepsin‐resistant fragment is degraded forming two triple‐helical segments, the disulfide‐linked fragment P3 and the cysteine‐free fragment P1 containing chains with molecular weights of 72000 and 55000 respectively. The other fragments (P2, P3B and P3C) were recovered at lower yields and may originate from a second, genetically distinct type of basement membrane collagen. This interpretation is supported by partial amino acid sequence analysis of the two non‐disulfide‐linked fragments (P1, P2). These sequences show that P1 and P2 are different and start with a non‐helical sequence followed by the helical triplet structure Gly‐X‐Y. Studies on pepsin fragments of the insoluble tumor collagen demonstrated a pattern similar to that obtained with the soluble form except for the occurrence of disulfide‐linked α‐chain‐like material. These chains also have an amino acid composition characteristic for basement membrane collagen. Taken together, the findings suggest that the tumor produces several related collagens. Copyright © 1979, Wiley Blackwell. All rights reserved