A unique, pepsin-sensitive collagen synthesized by aortic endothelial cells in culture

A unique collagen, designated EC, has been isolated from the culture medium of adult bovine aortic endothelial cells. After diethylaminoethylcellulose chromatography of [3H]proline-labeled culture medium, three non-disulfide-bonded bacterial collagenase-sensitive components with apparent Mr of 177000 (EC 1), 125000 (EC 2), and 100000 (EC 3) were demonstrated. Molecular sieve chromatography, cyanogen bromide cleavage, and two-dimensional peptide mapping of radioiodinated EC fragments produced by protease digestion suggest that the lower molecular weight components originate from EC 1. Both EC 1 and EC 2 were digested by pepsin within 10 min to products of less than 60000 molecular weight, under conditions which supported only limited proteolysis of other native collagens. A pepsin-resistant fragment of Mr 50000, derived from a digest of EC 2, contained equal amounts of hydroxyproline and proline, suggesting that at least a portion of the endothelial collagen contains a stable, collagen-like triple helix. Comparative mapping using mast cell protease and cyanogen bromide cleavage, followed by polyacrylamide gel electrophoresis, indicates that the primary structure of this collagen differs from that of other known collagen types.