Self-diffusion and self-association of lysozyme molecules in solution

Self-diffusion of lysozyme molecules at the process of their self-association were studied by pulsed-field gradient nuclear magnetic resonance (NMR) at different lysozyme concentrations in solution. It was shown that in the intervals of pH from 1.8 to 4.0 and from 6.5 to 9.0, lysozyme self-diffusion coefficients were independent of pH value. In the interval of pH from 4.0 to 6.5, they decreased with increasing pH. Using self-diffusion data, estimations of the equilibrium constant k of the self-association reaction were made. For the model of indefinite self-association, k was found to be 264.5 +/- 0.5 l/M, and for its particular case-dimerization, 143 +/- 0.5 l/M. The dependence of the concentration of monomers and different associates on the total protein concentration was calculated.