The self‐assembly of collagen molecules

The aggregation of native acid‐soluble collagen (N‐ASC) and of pronase‐treated acid soluble collagen (P‐ASC) was examined in solution under conditions which varied from those of minimum collagen‐collagen interaction to those leading to incipient fiber formation. Molecular weights and weight distributions were determined in the analytical ultracentrifuge using the Yphantis high speed sedimentation equilibrium and Aarchiblad approach‐to‐equilibrim techniques. The aggregation was pH and ionic strength dependent in each case. Under conditions of minimum aggregation (low pH, low ionic strength), N‐ASC showed the presence of permant aggregates. At higher pH and ionic strength, a higher fraction of aggregate was formed but these were of the same charcter and molecular weight as the permanent aggregates. The aggregates were of a single molecular size, with a weight of 1.5 × 10⁶ daltons, compared with a monomer collagen weight of 3.1 × 10⁵ daltons. The P‐ASC formed aggregates also but to a much lower extent and the maximum aggregate size corresponded to dimers in molecular weight. These data show the major importance of molecular end‐regions in collagen aggregation to form native type fibers and, by virtue of the discrete size of the N‐ASC aggregates, support the microfibrillar hypothesis for the assembly of collagen fibrills.