Protection of ceruloplasmin by lactoferrin against hydroxyl radicals is pH dependent.

Destruction of ceruloplasmin (Cp) in the presence of hydrogen peroxide is accompanied by the release of the protein's copper ions that provoke formation of hydroxyl radicals (OH˙) and, consequently, further degradation of the protein. Under such conditions, degradation of Cp is hampered by a number of substances able to bind copper ions. Lactoferrin (Lf) is the most active protector of Cp, its protective effect depending on the pH of the medium. The best protection of Cp by Lf was detected at pH 7.4. In an acidic buffer (pH 5.5), Lf did not affect the destruction of Cp. The pH-dependent efficiency of copper binding by Lf is in good agreement with its capacity to protect Cp against degradation provoked by hydrogen peroxide. It seems likely that peroxide-dependent degradation of Cp stimulated by its own copper ions is a part of neutrophil-induced antimicrobial reactions and may take place properly at the foci of inflammation. Interaction of Lf with Cp may regulate the generation of OH˙ from hydrogen peroxide in the foci of inflammation and protect the adjacent tissues.

Prion-associated proteins in yeast: comparative analysis of isogenic [PSI(+)] and [psi(-)] strains.

A large group of prion-associated proteins was identified in yeast cells using a new approach, comparative analysis of pellet proteins of crude cell lysates in isogenic strains of Saccharomyces cerevisiae differing by their prion composition. Two-dimensional (2D) electrophoresis followed by MALDI analysis of the pellet proteins of [PSI(+)] and [psi(-)] strains after prion elimination by GuHCl and prion transmission by cytoduction permitted identification of ca. 40 proteins whose aggregation state correlated with the change of prion(s) content. Approximately half of these proteins belonged to chaperones and to enzymes of glucose metabolism. Chaperones are known to be involved in prion metabolism and are expected to be present in prion-containing aggregates, but glucose metabolism enzymes are not predicted to be present. Nevertheless, several recent data suggest that their presence is not incidental. We detected six proteins involved in oxidative stress response and eight in translation. Also notable is a protease. Most of the identified proteins seem to be prion-associated, but we cannot exclude the possibility that several proteins may propagate as prions.

Studies of the ceruloplasmin-lactoferrin complex.

We have previously shown that iron-containing human lactoferrin (LF) purified from breast milk is able to form both in vitro and in vivo a complex with ceruloplasmin (CP), the copper-containing protein of human plasma. Here we present evidence that the CP-LF complex is dissociated by high concentrations of NaCl, CaCl2, or EDTA, or by decreasing the pH to 4.7. In addition, DNA, bacterial lipopolysaccharide, and heparin can displace CP from its complex with LF. Antibodies to either of the two proteins also cause dissociation of the complex.