The aggregation behavior of zinc-free insulin studied by small-angle neutron scattering

Abstract

The aggregation behavior of zinc-free insulin has been studied by small-angle neutron scattering as a function of pH and ionic strength of the solution. The pair distance distribution functions for the 12 samples have been obtained by indirect Fourier transformation. The results show that the diameter of the aggregates is 40 A at pH 11 and 10 mM NaCl, independent of the protein concentration. The largest diameter of about 120 A is found for pH 8, 100 mM NaCl, and a protein concentration of 10 mg/ml. Estimates of the pair distance distribution functions, free of inter-particle correlation effects, were obtained by an indirect Fourier transformation, omitting the data at small scattering vectors, which are influenced by these effects. By this procedure the weight-averaged molecular mass and the average radius of gyration were determined. These parameters vary from 1.3 times the monomer mass and 14 A, to 6.8 times the monomer mass and 31 A, respectively. The mass distribution between the oligomers was determined by a model based on the crystal structure of zinc-free insulin. The results from this model and the Fourier transformations have been compared to an equilibrium model recently introduced by Kadima et al. (1993). The neutron scattering results agree well with the predictions of this model except that broader mass distributions are suggested by neutron scattering.

Association behavior of native ?-lactoglobulin

“…where C is the protein concentration (g mL Ϫ1 ), N A is Avogadro's number, and ⌬ is the excess scattering length per unit mass (Da) of the protein (⌬ϭ Ϫ4.06 10 Ϫ14 cm Da Ϫ1 , which is a common value for proteins 40,41 ). The z-averaged radius of gyration R g,av can be calculated from the pair-distance distribution function according to…”

“…For obtaining the pair-distance distribution function, p(r) we used the IFT method of Glatter, 35 with some modifications as described by Pedersen et al 40 Effects due to noise, instrumental smearing, and truncation are eliminated by the IFT. The p(r) function is approximated by a sum of cubic spline functions, which are defined in the range 0 Յ r Յ D max .…”

“…For insulin a value of 0.45 has been reported. 40 The ␤-lg dispersions are not monodisperse and the large value of ␣ indicates that the oligomer structures of ␤-lg are rather open. The value for R g of the ␤-lg octamer of 35.4 Å found by Witz et al 21 does not correspond to our findings (see Figure 6).…”

Structure of PEP–PEO block copolymer micelles: exploiting the complementarity of small-angle X-ray scattering and static light scattering

“…In addition to the modelling described in detail in the previous section, the indirect Fourier transformation (IFT) method (Glatter, 1977;Pedersen et al, 1994) was used for obtaining model-independent information on the micelles. The IFT method provides the pair distance distribution function p(r), which is a histogram of all distances between point pairs within the particles weighted by the excess electron density (which can be both positive and negative) at the points.…”

Paradoxical Inhibition of Protein Aggregation and Precipitation by Transglutaminase-catalyzed Intermolecular Cross-linking

“…Fine balancing of the intermolecular forces of proteins in biological fluids may realize a variety of physical states, such as dispersed, equilibrium clustered, glass-like, or crystal states, as in pure solutions (3)(4)(5)(6)(7), because biological environments are highly diverse. Investigation of the factors that affect the intermolecular interactions of proteins are of primary importance from a biological viewpoint.…”