Biosynthesis of cartilage procollagen. Influence of chain association and hydroxylation of prolyl residues on the folding of the polypeptides into the triple-helical conformation.
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Cells isolated by enzymic digestion of embryonic cartilage were used to study the biosynthesis of type II procoliagen. The results demonstrated that interchain disulfide bonds among the three pro-a chains were not synthesized until well after assembly of amino acids into the polypeptide chains was completed. Also, the collagen portion of the molecule did not fold into a stable triple-helical structure which resisted pepsin digestion until well after assembly of the polypeptide chains was completed. In contrast, prolyl residues in the pro- chains were maximally hydroxylated before the synthesis of interchain disulfide bonds and helix formation. The results indicated therefore that the rate of helix formation during biosynthesis under the incubation conditions employed was not limited by the synthesis of hydroxyproline but appeared to be limited by chain association. For reasons which were not apparent, chain association and helix formation occurred at a later stage in cartilage cells synthesizing type II procollagen than in tendon cells synthesizing type I procollagen. In further experiments cartilage cells were incubated under anaerobic conditions so that they synthesized and retained protocollagen which was comprised of nonhydroxylated pro- chains largely linked by interchain disulfide bonds. When the cells were subsequently exposed to atmospheric O2, the rate of helix formation closely paralleled the hydroxylation of prolyl residues, indicating that after temporary anoxia synthesis of hydroxyprolyl residues limited helix formation. 1974, American Chemical Society. All rights reserved.
