title: Sedimentation equilibrium in a solution containing an arbitrary number of solute species at arbitrary concentrations: theory and application to concentrated solutions of ribonuclease.
abstract: Simple expressions are derived describing the equilibrium concentration gradient of each species in a solution containing an arbitrary number of solute species at arbitrary concentration, as a function of the concentration of all species. Quantitative relationships between the species gradients and experimentally observable signal gradients are presented. The expressions are model-free and take into account both attractive and repulsive interactions between all species. In order to analyze data obtained from strongly nonideal solutions, a statistical thermodynamic model for repulsive solute-solute interactions is required. The relations obtained are utilized to analyze the dependence of the equilibrium gradient of ribonuclease A in phosphate-buffered saline, pH 7.4, upon total protein concentration. Experimental results are interpreted in the context of a model for weak self-association leading to the formation of significant amounts of oligomers at total protein concentrations exceeding 25 g/l.
authors.affiliation: Instituto de Química Física Rocasolano, CSIC, Madrid, Spain.
authors.forename: Silvia
authors.initials: S
authors.lastname: Zorrilla
authors.forename: Mercedes
authors.initials: M
authors.lastname: Jiménez
authors.forename: Pilar
authors.initials: P
authors.lastname: Lillo
authors.forename: Germán
authors.initials: G
authors.lastname: Rivas
authors.forename: Allen P
authors.initials: AP
authors.lastname: Minton
mesh_terms: D001288:Attention; D019281:Dimerization; D006863:Hydrogen-Ion Concentration; D008954:Models, Biological; D008970:Molecular Weight; D011506:Proteins / Q000737:chemistry; D012259:Ribonuclease, Pancreatic / Q000737:chemistry*; D012996:Solutions / Q000737:chemistry; D013816:Thermodynamics; D014461:Ultracentrifugation / Q000379:methods
chemical_list: D011506:Proteins; D012996:Solutions; D012259:Ribonuclease, Pancreatic