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

Collagen synthesis and deposition in the predentine of the continuously erupting rat incisor was analyzed in vivo following a single intraperitoneal injection of [14C]glycine. Newly synthesized collagen was extracted from the dissected predentine with a solution of 1.0 m sodium chloride 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 over 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. However, from the ratio of the alpha 1 (I): alpha 2 it was estimated that approximately 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 fractions analyzed. From the profiles of isotope incorporation into collagens and collagen precursors, it was evident that collagen synthesis and processing was 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 in the salt-insoluble fraction and the appearance of beta and gamma chains as early as 30 min after 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.