The appearance of free hydroxyproline as the major product of degradation of newly synthesized collagen in cell culture.

Embryonic lung fibroblasts and rabbit vascular smooth muscle cells have the ability to degrade newly synthesized collagen. Analysis of 24-h pulse media from cultures given [14C]proline demonstrates that greater than 90% of the degraded collagen is represented by free hydroxyproline rather than the peptide-bound imino acid. The addition of cycloheximide or alpha-alpha-dipyridyl to the culture medium during the pulse period severely diminished the formation of the free hydroxyproline demonstrating its enzymatic and protein (collagen) origin. It is proposed that assessment of free hydroxyproline formation may allow us to distinguish between intracellular and extracellular collagen degradation.