title: Conformational changes in iota- and kappa-carrageenans induced by complex formation with bovine beta-casein.
abstract: The formation of electrostatic complexes between beta-casein and iota- and kappa-carrageenans is well-known. However, the molecular mechanism of the complexation has yet to be determined, particularly with respect to the conformational changes of the interacting macromolecules. High-sensitivity differential scanning calorimetry was used to study beta-casein/carrageenan mixtures at different pH values (3.0 to 7.5), ionic strengths (0.03 and 0.15 M), and various molar protein/polysaccharide ratios (3-400). The effects of these variables on the temperature, enthalpy, and width of the helix-coil transition of iota- and kappa-carrageenans were investigated. Neither pH nor the protein/polysaccharide ratio influenced the transition temperature of either carrageenan in the complexes. However, the transition enthalpy of both carrageenans in complexes with beta-casein decreased to zero with both decreasing pH and increasing protein/polysaccharide ratio. This may reflect an unwinding of the polysaccharide double helix induced by beta-casein, a conformational change which is fully reversible in conditions of sufficiently high ionic strength. The interaction of beta-casein with iota- and kappa-carrageenans was approximated in terms of the model of binding of large ligands to macromolecules, that provides the binding constants for these biopolymers.
authors.affiliation: N.M. Emanuel Institute of Biochemical Physics, Russian Academy of Sciences, Vavilov St. 28, 119991, Moscow, Russia. burova@ineos.ac.ru
authors.forename: Tatiana V
authors.initials: TV
authors.lastname: Burova
authors.forename: Natalia V
authors.initials: NV
authors.lastname: Grinberg
authors.forename: Valerij Ya
authors.initials: VY
authors.lastname: Grinberg
authors.forename: Anatoly I
authors.initials: AI
authors.lastname: Usov
authors.forename: Vladimir B
authors.initials: VB
authors.lastname: Tolstoguzov
authors.forename: Cornelis G de
authors.initials: CG
authors.lastname: Kruif
mesh_terms: D000818:Animals; D002152:Calorimetry, Differential Scanning; D002236:Carbohydrate Conformation; D002351:Carrageenan / Q000737:chemistry* / Q000378:metabolism; D002364:Caseins / Q000378:metabolism*; D002417:Cattle; D006863:Hydrogen-Ion Concentration; D009994:Osmolar Concentration; D044367:Phase Transition; D011485:Protein Binding; D055672:Static Electricity; D013696:Temperature; D013816:Thermodynamics
chemical_list: D002364:Caseins; D002351:Carrageenan