Evidence that chick tendon procollagen must be denatured to serve as substrate for proline hydroxylase.

The ability of chick-embryo proline hydroxylase to hydroxylate [(14)C]proline-labelled procollagen was investigated between 23 degrees and 37 degrees C. The amount of hydroxy[(14)C]proline that could be formed increased sharply between 26 degrees and 30 degrees C. This corresponded to the temperature interval in which the [(14)C]procollagen substrate was thermally denatured, and the results therefore indicate that only denatured molecules can be hydroxylated.