(1) A newly developed apparatus for the performance of automated batch light scattering measurements, with special application for the characterization of the concentration dependence of scattering intensity in highly concentrated protein solutions, initially described in last year's report, has been further improved. (2) Using the newly developed apparatus, the concentration-dependent scattering of three globular proteins, BSA, ovalbumin, and ovomucoid, and binary mixtures of all three proteins has been measured at concentrations of up to 120 g/L. The concentration dependence of scattering in solutions of both pure protein and binary mixtures may be satisfactorily described over the entire range of concentration by a model in which each species is represented by an equivalent hard spherical particle, the size of which reflects both hard steric and soft repulsive intermolecular interactions. (3) Using the newly developed apparatus, the concentration-dependent scattering of chymotrypsin A has been measured at concentration up to > 60 g/L at three different pH values. The concentration dependence may be described by an effective hard sphere model that allows for the equilibrium association of monomeric chymotrypsin A to form a dimer and a pentamer or hexamer depending upon pH. (4) The concentration dependence of light scattering of solutions of two different monoclonal IgGs over a concentration range of up to over 150 g/L at several different salt concentrations ranging from 40 to 600 mM NaCl has been analyzed in the context of an effective hard particle model allowing for equilibrium self-association. The data are well fit by an effective hard sphere model that allows for the equilibrium association of monomeric IgG to form a dimer and a tetramer, pentamer, or hexamer, depending upon salt concentration.
