Insoluble bovine corium collagen was dissolved in acid following a lyotropic swelling step at 25° and neutral pH at low ionic strength. The lyotropic swelling apparently relaxes interfibrillar bonding and permits the fibrils to swell without limit in acetic acid. Yields of soluble collagen were on the order of 20% of the total. The use of purified amylase or chelating agents did not increase the yields. Electron microscopic examination and intrinsic viscosity determination showed the soluble collagen to be present as very long thin filaments. CM-cellulose chromatography and disc electrophoresis of the denatured collagen indicated that the solubilized collagen was very highly cross-linked. These data support the concept of the limiting microfibrillar structure of collagen fibers and indicate that one main cross-linking system is entirely internal to the microfibrils.
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