1. We have simultaneously collected composition-dependent static and dynamic light scattering data on mixtures of non-interacting and interacting proteins, and developed a global analysis of the composition-dependence of both quantities. Contrary to expectation, addition of dynamic light scattering data did not enhance the resolution of characterization obtainable using static light scattering data only. Results of this work are being written up for publication. (B. Monterroso) 2. We have characterized the self-association equilibria of zinc-free insulin over a wide range of pH values, via measurement of the concentration dependence of static light scattering (A. Attri). At pH 1.6, insulin is a non-associating monomer in acetate buffer and a very weakly self-associating dimer in HCl. At pH values between 3 and 8, the concentration dependence of scattering is quantitatively accounted for by a simple isodesmic indefinite association scheme. At pH 10, the concentration dependence of scattering is quantitatively accounted for by a modified isodesmic scheme in which the equilibrium association constant for addition of monomer to monomer is about five times smaller than the equilibrium association constant for addition of monomer to all higher oligomers. A report of this work has been published (A. Attri, C. Fernandez). 3. We have characterized the self-association equilibria of insulin in the presence of zinc. Analysis of the concentration dependence of static light scattering indicates that over the concentration range studied (0.3 - 5 mg/ml), insulin behaves as a hexamer undergoing isodesmic indefinite self-association. Analysis of the concentration dependence of the dynamic light scattering confirms this interpretation. A report of this work has been published (A. Attri, C. Fernandez). 4. We have characterized the interaction between tau protein and a 7K molecular weight fraction of heparin, a sulfated polysaccharide with high negative charge density. The composition dependence of the scattering intensity is well described by a simple 1:1 heteroassociation. This is the first application of composition gradient - static light scattering to the association between two different types of macromolecule. A report of this work has been published (C. Fernandez, Y. Liang). 5. We have measured the dependence of the intensity of light scattering upon protein concentration in solutions of FtsZ containing either GTP an a GTP-regenerating system or GPCPP, a slowly hydrolyzable GTP analog, in the presence of varying concentrations of Mg++ ion. The simplest interpretation of the observed dependence is that self-association of either FtsZ-GTP or FtsZ-GPCPP proceeds initially by linear growtn according to an indefinite isodesmic scheme, followed by cooperative formation of a stable oligomer or narrow size distribution of oligomers of size 30-40 subunits that are thought to be cyclic. This work is being written up for publication (G. Rivas).
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