Electron microscopic demonstration of acid-labile, 4D-staggered intermolecular association of collagen formed in vitro.

The formation of acid-labile, unidirectional, and 4D-staggered dimers and polymers of collagen molecules in solutions at pH 4.0 and 4.5 has been demonstrated under the electron microscope. Collagen molecules extracted from lathyritic rat skin was dialyzed from 0.5 M acetic acid sequentially against 5-10 mM acetate buffer (pH 4-4.5) at 4 degrees C for 3-4 days, 0.3% glutaraldehyde in the same buffers for further 2 days, 0.5 M acetic acid, and then against 0.2% ATP X Na2/0.1 M acetic acid. Fibrous, unidirectional segment-long-spacing (SLS) forms were observed with 0.4D overlap between adjacent segments. Such a form was not observed when glutaraldehyde fixation step was omitted or when SLS was formed directly from the acidic solution; in both cases, monomeric SLS was only observed. It is concluded that collagen molecules, dispersed monomeric in acidic pH, form unidirectional linear dimers or polymers in which the molecules are associated with 0.4D overlap (4D stagger) at pH 4-4.5.