title: Protein-coated beta-ferric hydrous oxide particles. An electrokinetic and electrooptic study.
abstract: Using microelectrophoresis and electric light scattering techniques, we investigated the adsorption characteristics, surface coverage and surface electric parameters of superstructures from two isoforms of plastocyanin, PCa and PCb, in an oxidized state adsorbed on beta-ferric hydrous oxide particles. The surface electric charge and electric dipole moments of the composite particles and the thickness of the protein adsorption layer are determined in a wide pH range, at different ionic strengths and concentration ratios of PC to beta-FeOOH. The adsorption of the two proteins was found to shift the particles' isoelectric point and to alter the total electric charge and the electric dipole moments of the oxide particles to different extent. A "reversal" in the direction of the permanent dipole moment is observed at lower pH for PCb- than for PCa-coated oxide particles. Strict correlation is found between the changes in the electrokinetic charge of the composite particles and the variation in their "permanent" dipole moments. Data suggest that the adsorption of the proteins is driven by electrostatic and/or hydrophobic interactions with the oxide surfaces dependent on pH. The adsorption behaviour is consistent with the involvement of the "eastern" and "northern" patches of the plastocyanin molecules in their adsorption on the oxide surfaces that are differently charged depending on pH.
authors.affiliation: Institute of Biophysics, Bulgarian Academy of Sciences, Acad. G. Bonchev Str., Bl. 21, Sofia 1113, Bulgaria. aneli@obzor.bio21.bas.bg
authors.forename: A G
authors.initials: AG
authors.lastname: Dobrikova
authors.forename: M I
authors.initials: MI
authors.lastname: Dimitrov
authors.forename: S G
authors.initials: SG
authors.lastname: Taneva
authors.forename: I B
authors.initials: IB
authors.lastname: Petkanchin
mesh_terms: D000327:Adsorption; D020099:Coated Materials, Biocompatible; D004563:Electrochemistry / Q000379:methods*; D004586:Electrophoresis / Q000379:methods; D005290:Ferric Compounds / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D007526:Isoelectric Point; D007536:Isomerism; D008027:Light; D008956:Models, Chemical; D009994:Osmolar Concentration; D010316:Particle Size; D010970:Plastocyanin / Q000737:chemistry* / Q000493:pharmacokinetics*; D011487:Protein Conformation; D020033:Protein Isoforms / Q000737:chemistry; D011506:Proteins / Q000737:chemistry*; D012399:Rotation; D012542:Scattering, Radiation; D013499:Surface Properties
chemical_list: D020099:Coated Materials, Biocompatible; D005290:Ferric Compounds; D020033:Protein Isoforms; D011506:Proteins; C000499:ferric oxide; D010970:Plastocyanin