A study on ascorbate inhibition of ceruloplasmin ferroxidase activity

Oxidative Aggregation of Ceruloplasmin Induced by Hydrogen Peroxide is Prevented by Pyruvate

Ceruloplasmin (CP) is a blue copper glycoprotein with multiple physiological functions including ferroxidase and oxidase activities. CP is also an important serum oxygen free radical (OFR) scavenger and antioxidant, exerting cardioprotective and antifibrillatory actions. Although it has been reported that CP activities can be inhibited by OFR, the intimate mechanism of this inactivation is still not clear. Exposure of bovine CP to H2O2 induced inactivation of the protein as well as structural alterations as indicated by loss of protein bands by SDS-PAGE. Both phenomena were H2O2 concentration and time dependent. HPLC gel filtration and capillary electrophoresis analysis of CP treated with H2O2 revealed an aggregation of the protein. Quantification of dityrosine formation by fluorescence indicated the involvement of dityrosine bridging, which could be responsible for aggregation of CP under oxidative attack. Oxidative damage to CP under H2O2 treatment was completely prevented by pyruvate, suggesting that the association of CP with antioxidants could extend the range of the protective action of this protein.

Ferroxidases and xanthine oxidase in plasma of healthy newborn infants

In the neonatal period, there is a high iron load, while both the level and molar oxidase activity of ceruloplasmin are low. On the other hand, the neonatal xanthine oxidase (XO) activity is higher than later in life and XO has a significant iron-oxidizing capacity. We therefore studied the physiological contribution of XO to the ferroxidase activity of the plasma in 20 full-term newborn infants. Ferroxidase activity was measured spectrophotometrically, with Fe++ as substrate. The uric acid formed by XO was assayed by means of HPLC, with electrochemical detection. The total ferroxidase activity in the plasma was about one-fourth of the adult level and rapidly increased doubling within 3 days after birth. About 90% of the plasma ferroxidase activity was due to ceruloplasmin, the remainder being accounted for by ferroxidase II. The XO activity underwent a 30% (statistically non-significant) elevation at 24 h, though ferroxidase activity attributable to XO was not detected at any time. Accordingly, XO does not seem to add substantially to the total iron-oxidizing capacity of the plasma in the neonatal period. The high molar ferroxidase activity is probably of importance at the endothelial cell surface.