Light scattering Rayleigh linewidth measurements on some globular protein solutions

An apparatus previously described for investigating the Rayleigh linewidth of light scattered from macromolecular solutions by means of the optical homodyne technique has been modified so as to obtain the autocorrelation function of the fluctuations in scattered intensity. Its operation is described and some results presented for three commercially obtainable globular proteins: chymotrypsinogen, bovine plasma albumin and urease. Measurements were made in unbuffered 0.2M NaCl aqueous solutions and the diffusion constants, D_20w, found to be 7.4±0.3×10^?7cm²s^?1, 5.8±0.1×10^?7cm²s^?1 and 3.4±0.1×10^?7cm²s^?1 respectively. There was no detectable concentration dependence. In each case the results agreed well with theoretical predictions both as regards angular variation and shape of the autocorrelation function. The effects of polydispersity are discussed.