Role of Copper in Biosynthesis of Intramolecular Cross-links in Chick Tendon Collagen

Collagen was extracted from Achilles tendons of copper-deficient and control chicks by successive treatment with 0.15 m NaCl, 1.0 m NaCl, and 0.5 m acetic acid. The fractions extractable by 1.0 m NaCl and 0.5 m acetic acid were purified and characterized by ultracentrifugation and gel electrophoresis. They were then fractionated on carboxymethyl cellulose columns into their α1, α2, β11, and β12 components. These components were analyzed for amino acids and in part for aldehyde function. Copper deficiency not only increased the proportion of total extractable collagen but also markedly increased the proportion of α components at the expense of the β components. The α:β ratio was increased approximately 3-fold, and the β11 component was essentially eliminated. Copper deficiency had no detectable effect upon amino acid composition. The amino acid analyses confirmed the presence of two distinct polypeptide chains which occurred in a ratio of approximately 2:1. Both the salt-soluble and the acid-soluble collagen from copper-deficient tendons contained less aldehyde than those from control tissue. The control α1 component contained approximately 1 mole of aldehyde per 100,000 g, while the deficient α1 contained about 0.7 mole. Copper functions as a catalyst in the formation of the intramolecular bond in collagen and appears to be essential for formation of an intermediate aldehydic compound.