Non-caeruloplasmin copper and ferroxidase activity in mammalian serum. Ferroxidase activity and phenanthroline-detectable copper in human serum in Wilson's disease

Abstract

It is thought that 5-10% of human serum copper consists of copper ions complexed with histidine, amino acids or albumin. The phenanthroline assay developed by Gutteridge (Biochem. J. 218, 983-985; 1984) is shown to measure all these forms of copper down to a sensitivity of 0.1 mumol/dm3, yet it does not detect any copper ions in freshly-prepared serum or plasma from rats, mice, rabbits or guinea-pigs, or freshly-prepared serum from humans. It is concluded that the "non-caeruloplasmin copper pool" is much smaller than has previously been supposed. No phenanthroline-detectable copper could be measured in serum freshly prepared from four patients with uncomplicated Wilson's disease, but it could be measured in serum from a patient with fulminant hepatic failure. After liver transplantation, concentrations of phenanthroline-detectable copper in this patient fell to zero within two days. Studies on the ferroxidase activity of freshly-prepared serum or plasma samples shows that little ferroxidase II activity is present in samples from healthy adults or from the patient with Wilson's disease and fulminant hepatic failure. In all the patients, ferroxidase I activities are sub-normal. Freshly-prepared plasma or serum samples from several animal species generally show lower ferroxidase I and greater ferroxidase II activities than do human samples, but only in rabbits does ferroxidase II account for a high proportion of total plasma ferroxidase activity. Storage of biological fluids can cause release of copper from caeruloplasmin and a rise in ferroxidase II activity; these events may have confused some earlier studies.