Collagen metabolism in rat incisor predentine in vivo: synthesis and maturation of type I, .alpha.1 (I) trimer, and type V collagens

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Abstract
Collagen synthesis and deposition in the predentine of the continuously erupting rat incisor was analyzed in vivo following a single i.p. injection of [14C]glycine. Newly synthesized collagen was extracted from the dissected predentine with a solution of 1.0 M NaCl containing proteolytic enzyme inhibitors. Mature, cross-linked collagen was solubilized by limited pepsin digestion following extractions with 0.5 M acetic acid or 0.1 M penicillamine. Analysis of the radiolabeled collagens by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and fluorography showed that > 97% of collagen synthesized migrated in the .alpha.1 (I) and .alpha.2 positions following pepsin digestion; the remaining 3% migrated in the positions of .alpha.1 (V) and .alpha.3 (V) collagens. From the ratio of the .alpha.1 (I):.alpha.2 it was estimated that .apprx. 30% of the salt-extractable collagen was .alpha.1(I) trimer. The presence of this collagen was confirmed by salt-fractionation and cyanogen bromide digestion patterns. Type I, .alpha.1 (I) trimer and type V collagens were also found in the salt-insoluble tissue residue. In this fraction the .alpha.1 (I) trimer comprised 10-15% of the collagen measured as radioactivity but was difficult to discern colorimetrically. Type III collagen could not be detected in any of the fraction analyzed. From the profiles of isotope incorporation into collagens and collagen precursors, it was evident that collagen synthesis and processing were rapid. Processing of type I collagen and probably also .alpha.1 (I) trimer proceeded almost entirely through procollagen intermediates. Rapid maturation of the types I and V collagens was evident from the sharp increase in radiolabeled collagen in the salt-insoluble fraction and the appearance of .beta. and .gamma. chains as early as 30 min aftr isotope administration. Radiolabeled procollagens were also extracted with acetic acid and penicillamine, indicating that cross-linking of collagen precursors may be involved in fiber formation.