Synovial fluid from rheumatoid patients and normal cerebrospinal fluid contains micromolar concentrations of non-protein-bound iron salts that can promote lipid peroxidation and also the superoxide-dependent formation of hydroxyl radicals from hydrogen peroxide. These iron catalysts of oxygen radical reactions cannot be detected by conventional assays unless interfering high-molecular-weight substances, probably proteins, are removed by ultrafiltration or inactivated by exposure to low pH values. The bleomycin assay for ‘catalytic’ iron [Gutteridge, Rowley & Halliwell (1981) Biochem. J. 199, 263–265] does not suffer from these artifacts.
- © 1982 London: The Biochemical Society