Protocollagen proline hydroxylase (PPH) activity in skin was determined in vitro by radioassay employing a tritium-labeled L-proline-peptide substrate. Average PPH activity was significantly higher in biopsy specimens of both forearm and parasacral skin from 20 patients with scleroderma than in specimens from ten normal subjects and 17 patients with other diseases. These findings offer evidence that collagen synthesis is increased in the skin in scleroderma and suggest that assay of PPH activity in skin may be a useful tool for the diagnosis of this disease.
Keiser HR, Stein HD, Sjoerdsma A. Increased Protocollagen Proline Hydroxylase Activity in Sclerodermatous Skin. Arch Dermatol. 1971;104(1):57-60. doi:10.1001/archderm.1971.04000190059008