Effects of temperature on conformation, hydroxylation, and secretion of chick tendon procollagen.

When freshly isolated chick embryo tendon fibroblasts were incubated at 37” with [‘%]proline and 0.5 mM cy, CLdipyridyl, a ferrous iron chelator which inhibits prolyl hydroxylase, the labeled unhydroxylated procollagen molecules accumulated intracellularly. When pepsin digestion at 15” was used as an enzymatic probe of conformation, these molecules were shown to be non-triple helical, indicating that hydroxylation of proline is necessary for triple helix formation at normal body temperatures. When cells which had accumulated unhydroxylated procollagen at 37” were then incubated at 25”, large amounts of unhydroxylated procollagen were secreted into the medium. Although these secreted molecules were sensitive to pepsin they were shown to be largely triple helical when prolyl hydroxylase was used as another probe of collagen conformation. The retained molecules were shown to be largely non-triple helical by this same test. This result suggests that triple helix formation may be necessary for normal secretion of procollagen by these cells. When cells which had accumulated unhydroxylated procollagen at 37” were then incubated at different temperatures between 20’ and 37” in the presence of excess ferrous iron to reverse the ihhibition of prolyl hydroxylase, the accumulated molecules were secreted and the extent of hydroxyproline formation increased as the temperature during the reversal period increased. At 20’ less than 1% of the [14C]proline in the secreted molecules was hydroxylated while at 37” this value increased to 33 %. This result implies that under some conditions the body temperature of an organism may in part regulate the hydroxyproline content of the collagen molecules.