Production of procollagen by human fibroblasts in culture

Three hydroxyproline-containing proteins secreted into the medium by human fibroblasts in culture were isolated and characterized. A minor fraction was identical to the collagen monomer. The major fraction was a form of procollagen, which contained, in addition to pro alpha and alpha chains, a component estimated to have a molecular weight of 250,000. This component was a dimer of pro alpha chains joined by disulfide bonds. The third fraction, much lower in hydroxyproline and hydroxylysine content, was of still greater size. Pro alpha chains were released upon denaturation and reduction, indicating that this fraction may contain pro alpha chains linked by disulfide bonds to noncollagenous material.