Particle sizes of purified kappa-casein: metal effect and correspondence with predicted three-dimensional molecular models.
kappa-Casein as purified from bovine milk exhibits a rather unique disulfide bonding pattern as revealed by SDS-PAGE. The disulfide-bonded caseins present range from dimer to octamer and above and preparations contain about 10% monomer. All of these heterogenous polymers, however, self-associated into nearly spherical uniform particles with an average radius of 8.9 nm as revealed by negatively stained transmission electron micrographs. Evidence is presented that multivalent cations play a role in the stabilization of these spherical particles. Treatment with EDTA causes disruption of the kappa-casein particles and leads to a broder size distribution as judged by electron microscopy and dynamic light scattering. The size and shape of the particles are in accord with earlier proposed 3D models for kappa-casein that actually predicted participation of divalent cations in the structure.
USDA, ARS, Eastern Regional Research Center, Wyndmoor, Pennsylvania 19038, USA.
H M
HM
Farrell
T F
TF
Kumosinski
P H
PH
Cooke
G
G
King
P D
PD
Hoagland
E D
ED
Wickham
H J
HJ
Dower
M L
ML
Groves
D000596:Amino Acids / Q000032:analysis; D002118:Calcium / Q000032:analysis*; D002364:Caseins / Q000737:chemistry*; D004492:Edetic Acid / Q000494:pharmacology; D007501:Iron / Q000032:analysis*; D046911:Macromolecular Substances; D008854:Microscopy, Electron; D008958:Models, Molecular; D010316:Particle Size; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D017550:Spectroscopy, Fourier Transform Infrared
D000596:Amino Acids; D002364:Caseins; D046911:Macromolecular Substances; D004492:Edetic Acid; D007501:Iron; D002118:Calcium