Identification of two further collagenous fractions from articular cartilage

Salt fractionation of pepsin-solubilized human and porcine articular cartilage has revealed the presence of two further collagenous fractions, CF1 and CF2, at high salt concentration following the precipitation of Type-II, 1 alpha, 2 alpha, 3 alpha, and Type-M collagens. Both fractions precipitate at 2.0 M NaCl, but higher yields of CF1 are obtained at 3.0 M NaCl. CF1 and CF2 can be separated in the native form using carboxymethyl-cellulose chromatography. Under denaturing conditions, CF1 has an apparent molecular weight of 25 000 and is unaffected by mercaptoethanol, whereas CF2 has a molecular weight of 35 000 before and 12 000 after reduction by mercaptoethanol. These fractions are probably fragments derived from larger collagen molecules, although the cyanogen bromide digest studies suggest that they are derived from a collagenous type other than one of those previously identified in cartilage.