Caeruloplasmin: a plasma protein, enzyme, and antioxidant.

Multifunctional roles of the plasma protein, caeruloplasmin, have been briefly reviewed under three main headings. These are protein functions, enzymic activity, and antioxidant protection. As a plasma protein it is said to play a role in the transport of copper. Since some 95% of serum copper is associated with caeruloplasmin, measurement of the protein provides a useful guide to copper levels. Enzymic functions are related to its oxidase activity. Substrates commonly used for laboratory assay include non-biologically occurring aromatic amines and polyphenols. More recently, a physiological function has been proposed in which the enzyme oxidases iron from the ferrous to ferric state for binding to apotransferrin. This enzymic function of caeruloplasmin has been designated 'ferroxidase'. In vitro studies have shown that caeruloplasmin can inhibit the peroxidation of polyunsaturated fatty-acids. This function is in part related to its ferroxidase activity. No antioxidant activity has yet been demonstrated in vivo but this possibility is speculatively discussed.