Immunoreactive prolyl hydroxylase in human skin, serum and synovial fluid: changes in the content and components with age

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Abstract
The concentration of immunoreactive prolyl hydroxylase was measured in human skin, serum and synovial fluid. In skin concentrations of the immunoreactive enzyme protein and the enzyme activity were highest in foetuses, at an intermediate level in 0–1‐year‐old children and lowest in adults. About 13–19% of the enzyme protein in foetal skin was in the active form compared with 2–4% in the adult. Concentrations of immunoreactive prolyl hydroxylase in serum were lower than in skin and no changes were found with age. The concentration of immunoreactive prolyl hydroxylase in synovial fluid of the knee joint in patients with traumatic effusion was about half that found in serum.The ratio of enzyme tetramer, which is the active form of the enzyme, to the total immunoreactive protein was studied by gel filtration. In foetal skin, about 15–20% of the total immunoreactive protein was present in tetramer form, and a good correlation was found between the ratio of enzyme tetramer to the total immunoreactive protein and the ratio of enzymic activity to the concentration of total immunoreactive enzyme. Small amounts of enzyme tetramer were found in the serum and synovial fluid. The data suggest that the activity of prolyl hydroxylase in human tissues may be partly controlled by a mechanism involving changes in the ratio of the active enzyme tetramer to total enzyme protein.