The Formation of Triple‐Helical Collagen Molecules from α1 or α2 Polypeptide Chains

The triple‐helical collagen molecule of vertebrates consists of two or three non‐identical polypeptide chains: [(α1) 2 (α2)] or [(α1)(α2)(α3)]. We have attempted to form molecules from three identical chains: (α1) 3 or (α2) 3 . The yield of (α1) 3 ‐molecules obtained after renaturation of α1 from calf or rat skin collagen and the yield of [(α1) 2 (α2)]molecules after renaturation of unfractionated collagen from both species is almost the same. (α1) 3 ‐molecules are able to form fibrils of the native type and long‐spacing segments. Their melting temperature of approximately 34° is only slightly less than that of native molecules. In contrast the (α2) 3 ‐molecules is much less stable with a melting range of 20–24°. Therefore, (α2) 3 ‐molecules are formed at lower temperatures and with a lower yield than (α1) 3 ‐ and [(α1) 2 (α2)]molecules. Renaturation experiments with a mixture of α1 and α2 (ratio 2:1) shows that the reformation of the [(α1) 2 (α2)]molecule is favoured over the (α1) 3 ‐molecule, in spite of the fact that both molecule have almost the same stability. Long‐spacing segments from (α1) 3 , (α2) 3 or native [(α1) 2 (α2)]molecules exhibit a similar if not identical crossstriation pattern in the electron microscope. Therefore, the conclusion can be drawn that the α1 and α2 chains are homologous.