Type‐IV Collagens

Abstract

Two sets of structurally distinct collagen components resembling type IV collagen have been isolated and purified from the pepsin digest of kidney cortex homogenates. C and D chains with the size of α chains were separated from disulfide‐linked material on molecular sieves and were further purified by ion‐exchange chromatography. The molecular gel filtration of the starting material also gave two high‐molecular‐weight collageneous fractions. The reduction of these fractions with dithiothreitol followed by carboxymethyl‐cellulose chromatography resulted in the separation of two major peaks, one corresponding to C‐1 and the second peak corresponding to D‐1 and a 75000‐M_r components. These latter two components were further separated from each other by molecular sieve chromatography. In addition some smaller peptides (two 50000‐M_r and one 15000‐M_r peptides) were purified and analyzed. By amino acid composition, chromatographic properties and cyanogen bromide peptide patterns on sodium dodecyl sulfate/polyacrylamide gel electrophoresis, the C‐1 and C chains and one of the 50000‐M_r components appear to be derived from the same chain by pepsin cleavage at different sites. Similarly, the D1 and D chains, and the 75000‐M_r the second 50000‐M_r and the 15000‐M_r components are related to each other but are structurally distinct from the C‐1 and C components. The presented data are consistent with the presence of two structurally distinct chains in basement membrane collageneous molecules.