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

Journal Article · Tue Nov 01 00:00:00 EST 1988 · Arch. Biochem. Biophys.; (United States)

DOI:https://doi.org/10.1016/0003-9861(88)90288-3· OSTI ID:6583872

Kumosinski, T F; Pessen, H; Farrell, Jr, H M; Brumberger, H

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 and micellar 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 core and a loose 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. (Abstract Truncated)

• Research Organization: Department of Agriculture, Philadelphia, PA (USA)
• OSTI ID: 6583872
• Journal Information: Arch. Biochem. Biophys.; (United States), Vol. 266:2
• Country of Publication: United States
• Language: English

Related Subjects

59 BASIC BIOLOGICAL SCIENCES
CASEIN
MOLECULAR STRUCTURE
CALCIUM COMPOUNDS
CATTLE
COLLOIDS
MILK
POLYMERS
X-RAY DIFFRACTION
ALKALINE EARTH METAL COMPOUNDS
ANIMALS
BIOLOGICAL MATERIALS
BODY FLUIDS
COHERENT SCATTERING
DIFFRACTION
DISPERSIONS
DOMESTIC ANIMALS
FOOD
MAMMALS
MATERIALS
ORGANIC COMPOUNDS
ORGANIC PHOSPHORUS COMPOUNDS
PROTEINS
RUMINANTS
SCATTERING
VERTEBRATES
550201* - Biochemistry- Tracer Techniques