The effect of non-polar liquids and non-ionic detergents on the ultrastructure and assembly of rat tail tendon collagen fibrils in vitro.

Non-ionic detergents or emulsions of non-polar liquids when added to solutions of rat tail tendon collagen (RTTC) or to the dispersed fibrils produced similar conspicuous ultrastructural modifications in the form of a D-periodic lesion between bands c2 and d in the 'gap region' of the fibril close to the start of the overlap region. The size and extent of the lesion in some fibrils indicates that at least some of the collagen molecules rupture. In an attempt to detect peptide fragments produced in this way we ran SDS-PAGE gels of collagen fibrils treated with the non-ionic detergent Triton X-100. These contained two peptides (44 and 32 kDa) not seen in controls. The lesions are thought to result from interactions between the hydrophobic part of non-polar liquids or detergents with an anomalous part of the fibril's D-period. The anomalous region has a high concentration of hydrophobic and alanyl residues but exceptionally few charged and hydroxyproline ones. We suggest that the anomalous region may play a part in storing and dissipating strain energy and permitting cross-link formation. Similar collagen-lipid interactions may occur under pathological conditions.