[Isolation of stable human ceruloplasmin and its interaction with salmon protamine]

An interaction was discovered between ceruloplasmin (CP, a ferro-O2-oxidoreductase, EC 1.16.3.1), a copper-containing protein of human blood plasma, and salmon protamine (PR), a cationic polypeptide of vertebrates that provides a compact structure of spermatozoid DNA. Addition of PR to CP at a molar ratio of 2: 1 decreases the CP electrophoretic mobility. Two types of CP binding centers for PR were determined: two centers with a high (Kd1 of 5.31 x 10(-7) M) and four centers with a low affinity (Kd2 of 1.56 x 10(-5) M). PR was shown to form complexes with CPs of various animal species. The CP-PR complex dissociates at an increased ionic strength (0.3 M NaCl), at pH decreased below 4.7, or in the presence of added polyanions (DNA, lipopolysaccharides, or heparin) and/or polylysine, which indicates the electrostatic nature of the interaction. The CP-PR interaction increased 1.5-fold the rate of CP-catalyzed oxidation of Fe2+. The preliminary treatment of blood plasma with arginine-Sepharose and heparin-Sepharose (to remove the blood coagulation factors) and affinity chromatography on PR-Sepharose helped isolate the practically unproteolyzed monomeric CP in 90% yield; it remained stable for more than two months at 37 degrees C. The English version of the paper: Russian Journal of Bioorganic Chemistry, 2005, vol. 31, no. 3; see also http://www.maik.ru.