A Kinetic Study of Collagen Biosynthesis

Abstract

Abstract The kinetics of incorporation of [14C]glycine into the cyanogen bromide peptides of the α1 and α2 chains of pulse-labeled collagen was analyzed in a system of cranial bone (calvaria) from newborn rats. From the time dependence of the difference in specific activity between peptides in the same chain, it was estimated that the rate of translation of the mRNA for a collagen chain is about 209 residues per min and is approximately equal for both α1 and α2. The data indicate that hydroxylation and helix formation occur either during translation or very rapidly thereafter. It was determined that the samples consisted in part of collagen obtained by conversion of precursor (procollagen) during neutral salt extraction. The pro α1 chain from acid-extracted samples was found to have a molecular weight of 115,000 compared to 95,000 for an α 1 chain. The calculated assembly time for a pro α chain, and for a completed procollagen molecule, is then 6.0 min, assuming linear polypeptide chains of 1,250 residues and a constant translation rate. The kinetic analysis allows the prediction that the extra peptide material that is lost during conversion of procollagen is at the amino-terminal ends of the chains. The time previously calculated (Vuust, J., and Piez, K. A. (1970) J. Biol. Chem., 245, 6201) from pulse-labeling studies for the biosynthesis of a complete fully hydroxylated collagen molecule, 4.8 min, can now be seen to be an apparent value obtained as a result of the then unknown conversion of procollagen to collagen during extraction. Re-evaluation of those data leads to a biosynthesis time of 5.8 min for a procollagen molecule, in good agreement with the present study. The rate of conversion to collagen is not known.