A Sedimentation Equilibrium Study of the Interaction between Ovalbumin and Lysozyme

A method is outlined for the analysis of sedimentation equilibrium results obtained with macromolecular systems undergoing heterogeneous association. It involves the solution of a set of simultaneous equations describing the distribution at equilibrium of the total concentration as a function of radial distance, and leads to the evaluation of apparent association constants for specified complexes. It is shown that these values may be used to compute a plot of an apparent weight-average molecular weight versus total concentration which may be compared with experimental results in an attempt to define the nature of the complexes present. The method is applied to results obtained with different mixtures of ovalbumin and lysozyme in phosphate buffer of pH 6.8 and Γ/2 = 0.02. It is shown that at low total concentrations a 1:1 complex predominates, but as the concentration is increased higher order complexes form. The results are compared with previous findings derived from migration studies on the same system.