Role of molecular conformation on secretion of chick tendon procollagen.

Embryonic chick tendon fibroblasts were incubated under conditions which resulted in the intracellular accumulation of radioactively labeled procollagens differing in their hydroxyproline content and in their conformation. When cells were incubated with 1 PM colcemide, fully hydroxylated, triple helical procollagen accumulated intracellularly. Incubation with 100 pg/ml of the proline analogue azetidineZ-carboxylic acid resulted in accumulation of hydroxylated procollagen which had an abnormal conformation due to structural alterations in the peptide bonds at sites of proline replacement by the analogue. Cells incubated with 0.5 mM cu,cu’-dipyridyl accumulated unhydroxylated procollagen which was capable of undergoing temperature-dependent conformational changes, affecting a random coil conformation at 37” and reassembling into a triple helix at 24”. When the rates of secretion of the various procollagens were determined, it was found that fully hydroxylated and unhydroxylated procollagens were secreted at approximately the same rates at 24”, a temperature at which both kinds of procollagens were in a helical conformation. If the secretion was examined at 37”, the hydroxylated molecules were secreted at a markedly more rapid rate than the unhydroxylated molecules which were in a nonhelical conformation at this temperature. The analogue-containing procollagen was secreted at a slower rate than hydroxylated procollagen at 37” and also at a slower rate than unhydroxylated procollagen at 24”. The results indicate that the hydroxyproline content of the molecules does not determine their rate of secretion and suggest that a proper molecular conformation is the important factor.