The carboxylpropeptide of type I procollagen in skin fibrillogenesis.

Previous studies suggested that the aminopropeptide of type I procollagen may initiate fibril formation. The purpose of this investigation was to study the location of the carboxylpropeptide of type I procollagen during collagen fibrillogenesis. Chick embryonic and posthatching skin specimens were studied by immunofluorescence and immunoelectron microscopy and by immunoblotting with antibodies against the amino and carboxylpropeptide of type I procollagen. The carboxylpropeptide was demonstrated at the surface of collagen fibrils, 20-40 nm in diameter (10-day embryos) and in fibrils, 40-65 nm (21-day embryos). In addition, the carboxylpropeptide was found at the cell surface and free in the ground substance. The aminopropeptide was only seen in fibrils, 20-30 nm in diameter, as previously reported. Ratios of pN-collagen/pC-collagen increased from 16 days embryonic to 3 and 9 days postembryonic skins. This study suggests that both pN-collagen (aminopropeptide plus collagen) and pC-collagen (carboxylpropeptide plus collagen) participate in fibrillogenesis.