Some properties of neutral-salt-soluble collagen. 1

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Abstract
Neutral-salt-soluble collagen was extracted from the skins of young rabbits and rats and purified by repeated salting-out. The purification process was studied. This neutral-salt-soluble collagen was separated into 3 parts: (a) fraction A, which reversibly formed libers at 37[degree], the fibers dissolving again on cooling, (b) fraction B, which did not form fibers on warming to 37[degree], and (c) fraction C, which on warming to 37[degree] formed libers that did not dissolve on subsequent cooling. The proportions of these fractions were independent of concentration and pH over a limited range. Evidence for the existence of 3 fractions was obtained from a study of the effects of repeated warming and cooling. The original material and the separated fractions were investigated by sedimentation, viscosity and streaming birefringence analyses. No significant differences were found between the fractions. A representative particle was estimated as a highly elongated rod, several thousand Angstrom units long, with a particle weight of about 500,000. No differences in the hydroxyproline, proline or glycine contents of the separate fractions were found. Hexose and hexosamine contents were negligible. Neutral-salt-soluble collagen contained not more than one atom of phosphorus in a particle of 340,000 molecular-weight units. The phosphorus is probably present as an impurity.