1. The effect of guanidine hydrochloride (GuHCl) and trimethyl-N-amine oxide (TMAO) upon the equilibrium dissociation of tetrameric to dimeric cyanmethemoglobin (CNmetHb) was studied by measurement of dynamic light scattering. This measurement yields the intensity average diffusion coefficient of the protein, which increases as the protein dissociates. The results showed that the increasing tendency of CNmetHb to dissociate with added GuHCl may be inhibited by addition of sufficient amounts of TMAO. The stabilizing effect of TMAO is attributed largely to volume exclusion (D. Wu). 2. The self-association of the bacterial septation protein FtsZ in the presence of GTP or a GTP analogue, GMPCPP, and 500 mM potassium was studied as a function of protein and Mg concentration using single-angle and multi-angle static light scattering. The results reveal that when the concentration of protein exceeds a Mg-dependent critical value, FtsZ undergoes a concerted formation, akin to a second-order phase transition to a narrow distribution of high molecular weight oligomers with a stoichiometry of ca 100 (GTP) or 160 (GMPCPP). Above the transition concentration, the amount, but not the size, of oligomer increases, while that of low molecular weight species remains roughly constant (Monterroso, Rivas). All of the data obtained from the several types of measurements may be accounted for semiquantitatively in the context of a model, according to which the stable oligomer is a cyclic species, the size of which reflects the tendency of the protein fibrils to flex or curve in solution in the presence of different concentrations of Mg and the particular guanine nucleotide present (B. Monterroso, G. Rivas, CIB).

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Wu, Di; Minton, Allen P (2015) Quantitative characterization of nonspecific self- and hetero-interactions of proteins in nonideal solutions via static light scattering. J Phys Chem B 119:1891-8
Wu, Di; Minton, Allen P (2013) Compensating effects of urea and trimethylamine-N-oxide on the heteroassociation of α-chymotrypsin and soybean trypsin inhibitor. J Phys Chem B 117:3554-9
Wu, Di; Minton, Allen P (2013) Quantitative characterization of the interaction between sucrose and native proteins via static light scattering. J Phys Chem B 117:111-7
Wu, Di; Minton, Allen P (2013) Quantitative Characterization of the Compensating Effects of Trimethylamine-N-oxide and Guanidine Hydrochloride on the Dissociation of Human Cyanmethmoglobin. J Phys Chem B 117:9395-9
Monterroso, Begoña; Ahijado-Guzmán, Rubén; Reija, Belén et al. (2012) Mg(2+)-linked self-assembly of FtsZ in the presence of GTP or a GTP analogue involves the concerted formation of a narrow size distribution of oligomeric species. Biochemistry 51:4541-50
Fernández, Cristina; Minton, Allen P (2011) Effect of nonadditive repulsive intermolecular interactions on the light scattering of concentrated protein-osmolyte mixtures. J Phys Chem B 115:1289-93
Rivas, Germán; Minton, Allen P (2011) Beyond the second virial coefficient: Sedimentation equilibrium in highly non-ideal solutions. Methods 54:167-74
Fodeke, Adedayo A; Minton, Allen P (2010) Quantitative characterization of polymer-polymer, protein-protein, and polymer-protein interaction via tracer sedimentation equilibrium. J Phys Chem B 114:10876-80
Scherer, Thomas M; Liu, Jun; Shire, Steven J et al. (2010) Intermolecular interactions of IgG1 monoclonal antibodies at high concentrations characterized by light scattering. J Phys Chem B 114:12948-57
Attri, Arun K; Fernández, Cristina; Minton, Allen P (2010) pH-dependent self-association of zinc-free insulin characterized by concentration-gradient static light scattering. Biophys Chem 148:28-33

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