Cross-Linking of Collagen
The collagen molecules are stabilized in the fibrils by covalent intermolecular crosslinks, and these are vital for normal physiological function. The molecules of collagen are dispersed on hexagonal lattices in specifically staggered configurations to form fibrils. The covalent intermolecular cross-linking provides the fibrillar matrices with the tensile strength and viscoelastic physicochemical characteristics necessary to the performance of their various structural functions. The collagen cross-linking patterns are tissue-specific and probably are related to their individual physiological functions and not to the particular genetic type of collagen. Intermolecular cross-linking (iminium) occurs prior to intramolecular cross-linking (aldol) in type one collagen. D. Fujimoto demonstrated that achules tendon collagen contained a naturally occurring fluorescent cross-linking amino acid. Housley et al. isolated a stable nonreducible trifunctional cross-link from calf skin collagen. The cross-link was isolated from a large amount of unreduced mature bovine skin collagen and subjected to Fast Atom Bombardment Mass Spectrometry as well as 1H and 13C-Nuclear Magnetic Resonance.