Nature of the Collagenous Protein in a Tumor Basement Membrane

Abstract

The EHS sarcoma (named after its discoverer, Engelbreth‐Holm, and its primary characterizer, R. Swarm) contains an extracellular matrix of basement membrane. The collagenous component of the membrane was extracted with dilute acetic acid from tumors grown in lathyritic mice and separated from other proteins by chromatographic methods. This collagen has a composition resembling that reported for other basement membrane collagens. The polypeptide chains of the tumor collagen are linked by disulfide bonds and migrate after reduction intermediate between the α chains und β components of type‐I collagen. The circular dichroism spectra obtained from it resemble those obtained from other collagens. The intact protein contained about 280 residues of glycine per 1000 residues. After reduction of disulfide bonds in the basement membrane collagen, treatment with either pepsin or trypsin gave rise to resistant fragments containing one‐third glycine. These fragments formed segment‐long‐spacing crystallites 210 nm long in the case of those treated with pepsin and 350 nm long in the case of those treated with trypsin. The band pattern differs from that found with other collagens. Antibodies prepared against the tumor collagen were found to localize to the tumor matrix and to known basement membranes occurring in mouse tissues. The data suggest that these basement membranes may contain a collagenous protein similar to the tumor protein.