Variations in the Diameter of Collagen Fibrils, Bound Hexose and Associated Glycoproteins in the Intervertebral Disc

In attempting to explain the different physical characteristics of collagen in various tissues, a number of possibilities have been proposed. These include variations in glycosaminoglycans, more firmly associated “structural glycoproteins” (Robert and Robert, 1967) and collagen hexose contents (Spiro, 1969; Grant et al., 1969). The location of the hexose on specific hydroxylysine residues may hinder the formation of intermolecular cross-links (Morgan et al.. 1970), possibly imposing a limit on fibril diameter. Analyses of different layers of bovine skin indicate that coarser fibres are characterised by an increased dermatan sulfate: hyaluronic acid ratio (Hoffman et al., 1957). This arises mainly from a deficiency in hyaluronic acid because, contrary to previous statements, the dermatan sulfate remains approximately constant (Pearson, 1970). Keratan sulfate may be implicated in the formation of very thin fibrils found in more transparent tissues like cornea and nucleus pulposus.