Collagen
Around 30% of bone is composed of organic compounds, of which 90 to 95% is collagen, the rest being non-collagenous proteins. Collagen is a fibrous protein which provides the bone with strength and flexibility, and is an important component of many other tissues, including skin and tendon. Individual collagen molecules contain three polypeptides of about 1000 amino acids per chain with a high glycine and hydroxyproline content. Bundles of these collagen molecules are arranged in fibrils with a molecular weight close to 97.1 Daltons. These fibrils are twisted into a right handed coil (fibre) with a total weight of between 95000 and 102 000 Daltons (Waterlow et al. 1978:512; Woodhead-Galloway 1980:1-3, 23; Garlick 1969:504; Smith et al. 1983:211-12).
For the collagen fibre to fully mature a number of chemical bonds must form. These include hydrogen bonds involving hydroxyproline, which stabilise the helix, and cross linkages involving hydroxylysine and lysine, which stabilise the fibrillar structure (Smith et al. 1983:447). These processes occur throughout the growth and maturity of an individual, consequently the density and stability of the bone tends to increase while the solubility decreases (Waterlow et al. 1978:512-14; Hare 1980:209; Smith et al. 1983:450). Once these bonds form only a small fraction of collagen can be extracted by neutral salt solutions and organic acids or acid-citrate buffers. The insoluble collagen which remains from such dissolutions, can however, be solubilised by heating above 58'C. At this temperature the triple helix denatures, but will partly reform into a gel when cooled (Waterlow et al. 1978:512; Woodhead-Galloway 1980:55; Smith et al. 1983:215).
Collagen in its unaltered state is also very resistant to proteolytic enzymes, however a group of enzymes exist which degrade native collagen fibrils under physiological conditions of temperature and pH; these are the collagenases (Waterlow 1978:516; Smith et al. 1983:223). An enzyme secreted by the gas gangrene bacteria (Clostridium perfringens and Cl. histolyticum) and Bacteroides melaninogenicus, a bacterium common in the gingival crevice of the tooth, will also cleave the triple helix (Woodhead-Galloway 1980:59). The peptide's produced in such cleavage are then open to proteolytic attack from the more conventional enzymes (Waterlow 1978:516).
Around 30% of bone is composed of organic compounds, of which 90 to 95% is collagen, the rest being non-collagenous proteins. Collagen is a fibrous protein which provides the bone with strength and flexibility, and is an important component of many other tissues, including skin and tendon. Individual collagen molecules contain three polypeptides of about 1000 amino acids per chain with a high glycine and hydroxyproline content. Bundles of these collagen molecules are arranged in fibrils with a molecular weight close to 97.1 Daltons. These fibrils are twisted into a right handed coil (fibre) with a total weight of between 95000 and 102 000 Daltons (Waterlow et al. 1978:512; Woodhead-Galloway 1980:1-3, 23; Garlick 1969:504; Smith et al. 1983:211-12).
For the collagen fibre to fully mature a number of chemical bonds must form. These include hydrogen bonds involving hydroxyproline, which stabilise the helix, and cross linkages involving hydroxylysine and lysine, which stabilise the fibrillar structure (Smith et al. 1983:447). These processes occur throughout the growth and maturity of an individual, consequently the density and stability of the bone tends to increase while the solubility decreases (Waterlow et al. 1978:512-14; Hare 1980:209; Smith et al. 1983:450). Once these bonds form only a small fraction of collagen can be extracted by neutral salt solutions and organic acids or acid-citrate buffers. The insoluble collagen which remains from such dissolutions, can however, be solubilised by heating above 58'C. At this temperature the triple helix denatures, but will partly reform into a gel when cooled (Waterlow et al. 1978:512; Woodhead-Galloway 1980:55; Smith et al. 1983:215).
Collagen in its unaltered state is also very resistant to proteolytic enzymes, however a group of enzymes exist which degrade native collagen fibrils under physiological conditions of temperature and pH; these are the collagenases (Waterlow 1978:516; Smith et al. 1983:223). An enzyme secreted by the gas gangrene bacteria (Clostridium perfringens and Cl. histolyticum) and Bacteroides melaninogenicus, a bacterium common in the gingival crevice of the tooth, will also cleave the triple helix (Woodhead-Galloway 1980:59). The peptide's produced in such cleavage are then open to proteolytic attack from the more conventional enzymes (Waterlow 1978:516).
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