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Evidence for an amino-terminal extension in high-molecular-weight collagens from mature bovine skin.

Insoluble, mature collagen fibers from bovine skin have been partially solubilized by mild, denaturing, but nonhydrolytic means. The soluble denatured collagen was fractionated by alcohol coacervation, and a fraction rich in high-molecular-weight alpha-chains was obtained. The heavy alpha-chains were isolated by carboxymethylcellulose chromatography. Renaturation, followed by measurements of optical rotation at 365 nm, showed that stable, in-register renaturation was more readily accomplished in mixtures of heavy alpha-chains than in alpha1-beta(11)-chain mixtures. Renatured heavy alpha-chain preparations were precipitated in SLS form, negatively stained, and examined by electron microscopy. The SLS precipitates were compared with SLS segments from native soluble collagen and were found to match in band pattern and spacing along their entire length from the COOH-terminal region, except for an NH(2)-terminal extension of 170 +/- 30 A in the heavy alpha-chain SLS. The heavy alpha-chains correspond chromatographically with those previously reported to be intermediates in the conversion of procollagen to collagen, on the basis of their molecular weight and of labeling studies. The presence of NH(2)-terminal extensions, and their existence in mature insoluble collagen, suggest that these intermediates may have a special role in fibril formation.