Cross‐Linkages in Collagen

Three different types of intermolecular bonds were demonstrated to be present in calf collagen. Side‐to‐side bond: this fixes the quarter staggered array of the molecules within the fibrils and can casily be cleaved by pepsin. Head‐to‐tail bond: this connects molecules by their dissimilar ends, is located in the region of the 30 nm overlap, and is relatively pepsin resistant. End‐to‐end bond: this links adjacent molecules by their like ends, is located in terminal regions of the molecules, and can be easily cleaved by pepsin. Polymeric molecules which were connected solely by end to‐end bonds were extracted from calf skin collagen. Brief treatment with pepsin cleaved side‐to‐side and end‐to‐end bonds in calf Achilles tendon collagen and yielded polymeric molecules which were linked exclusively by head‐to‐tail bonds. Polymeric chains (γ‐ and higher components) were isolated by gel chromatography subsequent to denaturation of end‐to‐end and head‐to‐tail polymers. Polymeric molecules containing the original cross linkages could be reformed by renaturation of these polymeric chains.