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Biomedical subjects

H Brumberger

Publications and source records attributed to H Brumberger.

7 recordsLinked to original sources
PubMed1991

Tertiary and quaternary structural differences between two genetic variants of bovine casein by small-angle X-ray scattering.

The casein complexes of bovine milk consist of four major protein fractions, alpha s1, alpha s2, beta, and kappa. Colloidal particles of casein (termed micelles) contain inorganic calcium and phosphate; they are very roughly spherical with an average radius of 650 A. Removal of Ca2+ leads to the formation of smaller protein aggregates (submicelles) with an average radius of 94 A. Two genetic variants, A and B, of the predominant fraction, alpha s1-casein, result in milks with markedly different physical properties, such as solubility and heat stability. To investigate the molecular basis for these differences, small-angle X-ray scattering was performed on the respective colloidal micelles and submicelles. Scattering curves for submicelles of both variants showed multiple Gaussian character; data for the B variant were previously interpreted in terms of two concentric regions of different electron density, i.e., a "compact" core and a relatively "loose" shell. For the submicelle of A, there was a third Gaussian, reflecting a negative contribution due to interparticle interference. Molecular parameters for submicelles of both A and B are in agreement with hydrodynamic data in the literature. Data for the micelles, for which scattering yields cross-sectional information, were fitted by a sum of three Gaussians for both variants; for these, the corresponding two lower radii of gyration represent the two concentric regions of the submicelles, while the third reflects the average packing of submicelles within the micellar cross section. Most of the molecular parameters obtained showed small but consistent differences between A and B, but for submicelles within the micelle several differences were particularly notable: A has a greater molecular weight for the "compact" region of the constituent submicelle (82,000 vs 60,000) and a much greater submicellar packing number (6:1 vs 3:1). Reasons for these and other differences are to be sought in sequence differences and in differences in calcium-binding sites and charge distribution.

Animals↗
PubMed1988

Determination of the quaternary structural states of bovine casein by small-angle X-ray scattering: submicellar and micellar forms.

Whole casein occurs in milk as a spherical colloidal complex of protein and salts called the casein micelle, with approximate average radii of 650 A as determined by electron microscopy. Removal of Ca2+ is thought to result in dissociation into smaller noncolloidal protein complexes called submicelles. Hydrodynamic and light scattering studies on whole casein submicelles suggest that they are predominantly spherical particles with a hydrophobic core. To investigate whether the integrity of a hydrophobically stabilized submicellar structure is preserved in the electrostatically stabilized colloidal micellar structure, small-angle X-ray scattering (SAXS) experiments were undertaken on whole casein from bovine milk under submicellar (without Ca2+) and micellar (with added 10 mM CaCl2) conditions. All SAXS results showed multiple Gaussian character and could be analyzed best by nonlinear regression in place of the customary Guinier plot. Analysis of the SAXS data for submicellar casein showed two Gaussian components which could be interpreted in terms of a particle with two concentric regions of different electron density, designated as a "compact" (subscript C) core and a "loose" (subscript L) shell, respectively. The submicelle was found to have an average molecular weight of 285,000 +/- 14,600 and a mass fraction of higher electron density core, k, of 0.212 +/- 0.028. The radius of gyration of the core, RC, was 37.98 +/- 0.01 A with an electron density difference, delta rho C, of 0.0148 +/- 0.0014 e-/A3, while the loose region had values of RL = 88.2 +/- 0.8 A with delta rho L = 0.0091 +/- 0.0003 e-/A3. Calculated distance distribution functions and normalized scattering curves also were consistent with an overall spherical particle with a concentric spherical inner core of higher electron density. These results, and in particular the remarkably low electron densities of the shells, can be interpreted in terms of a loosely packed spherical aggregate stabilized by a hydrophobic inner core and surrounded by an even more loosely packed hydrophilic region, in agreement with the results of other studies. The SAXS data for the colloidal micellar casein, which yield only cross-sectional information related to a window of scattered intensity, were analyzed by a sum of three Gaussians with no residual function. The two Gaussians with the lower values of the radius of gyration were interpreted again as an indication of an inhomogeneous spherical particle of two electron densities with the same centroid.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1978

Mn2+-electron spin resonance spectra of several lectins.

Mn2+-ESR spectra of soybean, wax bean and lima bean agglutinin at Q- and X-band frequencies show nearly axially symmetric zero field splitting (ZFS); the dominant anisotropic term of the spin hamiltonian is the quadratic ZFS interaction. There is a relatively large distribution of ZFS parameters. No effects of specific inhibitor (N-acetylgalactosamine) on the soybean agglutinin spectrum were observed. The stoichiometric complex obtained on addition of Mn2+ to a Mn2+-free sample of this protein has a spectrum similar to that of the native protein. The small changes in the spectrum are interpreted in terms of a wider distribution of the ZFS parameters at the Mn binding site. Addition of Ca2+ to Mn2+-soybean agglutinin sharpens the lines, possibly because Ca2+ increases the rigidity of the complex.

Binding Sites↗
PubMed1974

Small-angle X-ray scattering of pig thyroglobulin in solution.

Small-angle X-ray scattering measurements on native pig thyroglobulin in phosphate buffer, pH6.9, yield a radius of gyration of 6.4nm (64A), a particle volume of approx. 1.5x10(3)nm(3) (1.5x10(6)A(3)), an axial ratio of 2.2:1 (assuming an ellipsoidal shape), and a solvation of 0.63g of solvent/g of protein.

Animals↗