Requirement of intact human ceruloplasmin for the glutathione-linked peroxidase activity

Structural integrity may be needed for the glutathione-linked peroxidase activity of human ceruloplasmin. Intact human ceruloplasmin has a potent peroxidase property to decompose H2O2 in the presence of reduced glutathione. However, the fragment of approximately 116000 Da produced by proteolytic degradation had less than one-third of the glutathione-linked peroxidase activity of intact ceruloplasmin. When further proteolysis occurred, glutathione-linked peroxidase activity of human ceruloplasmin disappeared. In contrast, ceruloplasmin (116000 Da and <96000 Da) fragmented by proteolysis significantly removed H2O2 irrespective of the presence of reduced glutathione. Although proteolytic fragmentation of ceruloplasmin occurs, the antioxidant activity of ceruloplasmin that prevents DNA strand breaks in a metal-catalyzed reaction system was significantly maintained.