Isolation and Characterization of New Collagens from Chick Cartilage

Three unique collagen chains were isolated from chick sternal cartilage following pepsin solubilization of total cartilage collagens and removal of the predominant type II collagen by fractional salt precipitation. Native molecules containing 1 alpha, 2 alpha and 3 alpha chains precipitated between 0.7 M and 1.2 M NaCl at acidic pH and could be purified by chromatography on carboxymethyl-cellulose and agarose columns. Although similar to mammalian 1 alpha, 2 alpha and 3 alpha chains, differences in the mobilities on sodium dodecylsulfate gel electrophoresis, CNBr peptide profiles and amino acid composition were found. The 1 alpha and 2 alpha chains resemble, but are structurally distinct from, the chick alpha 1(V) and alpha 2(V) chains. The 3 alpha chain appears to be closely related to the alpha 1(II) chain, although some differences in the cyanogen bromide peptides suggest that they might be different gene products. In addition, two collagenous fragments of Mr 140 000 (M1) and 35 000 (M2) were found which precipitated at 2.0 m NaCl at acidic pH. Both fragments contain interchain disulfide bonds. The larger fragment was reducible to subunits of approximate Mr 120 000, 48 000, 28 000 and 11 000. The smaller fragment gave rise to peptides of Mr about 12 000 and 10 000 after reduction. By the technique of rotary shadowing the native, unreduced larger fragment M1 appeared as a slender rod-like molecule with a distinct bend approximately 40 nm from one end. We interpret this finding as indicative of a focal amino acid sequence irregularity, disrupting the triple-helical conformation.