Effect of Lactoferrin on the Ferroxidase Activity of Ceruloplasmin

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A. V. Sokolov^*, M. O. Pulina, E. T. Zakharova, M. M. Shavlovski, and V. B. Vasilyev

Institute for Experimental Medicine, Russian Academy of Medical Sciences, ul. Akademika Pavlova 12, 197376 St. Petersburg, Russia; fax: (7-812) 234-9489; E-mail: biochem@nm.ru

^* To whom correspondence should be addressed.

Received September 21, 2004; Revision received November 19, 2004

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The effects of various forms of lactoferrin (Lf) interacting with ceruloplasmin (Cp, ferro-O₂-oxidoreductase, EC 1.16.3.1) on oxidase activity of the latter were studied. Comparing the incorporation of Fe³⁺ oxidized by Cp into Lf and serum transferrin (Tf) showed that at pH 5.5 apo-Lf binds the oxidized iron seven times and at pH 7.4 four times faster than apo-Tf under the same conditions. Apo-Lf increased the oxidation rate of Fe²⁺ by Cp 1.25 times when Cp/Lf ratio was 1 : 1. Lf saturated with Fe³⁺ or Cu²⁺ increased the oxidation rate of iron 1.6 and 2 times when Cp to holo-Lf ratios were 1 : 1 and 1 : 2, respectively. Upon adding to Cp the excess amounts of apo-Lf (Cp/apo-Lf < 1 : 1) or of holo-Lf (Cp/holo-Lf < 1 : 2) the oxidation rate of iron no longer changed. Complex Cp-Lf demonstrating ferroxidase activity was discovered in breast milk.

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KEY WORDS: ceruloplasmin, ferroxidase, lactoferrin, transferrin

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