On the mechanism of citrate inhibition of ceruloplasmin ferroxidase activity.

Ceruloplasmin is a plasma protein, which oxidizes ferrous ions in a catalytic manner. It is considered to function as a ferroxidase in vivo. Citrate was found to inhibit the reaction. The ceruloplasmin catalyzed oxidation of p-phenylenediamines, however, was not affected by citrate. The inhibitory effect is proposed to be due to formation of Fe(2+)-citrate, which does not react with ceruloplasmin. The stability constant for the Fe(2+)-citrate complex estimated from the present inhibition study is in good agreement with previously published data.