The monomer-dimer equilibrium of β-lactoglobulin B in acid solution has been studied by using the sedimentation equilibrium experiment. There is a quite general belief that, at combined chemical and sedimentation equilibrium, solution nonidealities cannot be taken into consideration, but in a recent series of papers Adams and collaborators have described a method by which such nonidealities are expressed and evaluated as activity coefficients, thus allowing for the computation of the equilibrium constants involved. Our experiments, designed to test this more comprehensive approach, required the determination of solute apparent weight-average molecular weights at a number of fixed concentrations and over wide concentration limits. The β-lactoglobulin B in solution at low pH values does provide a good test substance; it forms solutions in which monomer and its dimer are the predominant solute species in a solvent which under proper conditions can be considered as a single component. Pertinent theory is given in rather elementary form to describe the behavior of this simplest of associating systems. Using it for the interpretation of the data, numerical results for the activity coefficients and the equilibrium constant are obtained, tabulated, and discussed from the point of view of their uniqueness and meaning. © 1968, American Chemical Society. All rights reserved.
