Environmental effects on disulfide bonding patterns of bovine kappa-casein.
Bovine kappa-casein, the stabilizing protein of the colloidal milk protein complex, has a unique disulfide bonding pattern. The protein exhibits varying molecular sizes on SDS-PAGE ranging from monomer to octamer and above in the absence of reducing agents. Heating the samples with SDS prior to electrophoresis caused an apparent decrease in polymeric distribution: up to 60% monomer after 30 min at 90 degrees C as estimated by densitometry of SDS-PAGE. In contrast, heating the samples without detergent at 90 or 37 degrees C caused a significant increase in high-molecular-weight polymers as judged by electrophoresis and analytical ultracentrifugation. In 6 M urea, the protein could be completely reduced, but upon dialysis, varying degrees of polymer reformation occurred depending on the dialysis conditions. Spontaneous reoxidation to polymeric forms is favored at low pH (<5.15) and low ionic strength. The results are discussed with respect to the influence of the method of preparation on the polymer size of kappa-caseins and on their resultant physical chemical properties.
Groves
M L
ML
U.S. Department of Agriculture, ARS, Eastern Regional Research Center, Wyndmoor, Pennsylvania 19038, USA.
Wickham
E D
ED
Farrell
H M
HM
D000818:Animals; D001704:Biopolymers; D002364:Caseins / Q000737:chemistry* / Q000302:isolation & purification; D002417:Cattle; D004220:Disulfides / Q000737:chemistry*; D004591:Electrophoresis, Polyacrylamide Gel; D006358:Hot Temperature; D006863:Hydrogen-Ion Concentration; D010084:Oxidation-Reduction; D012967:Sodium Dodecyl Sulfate / Q000737:chemistry
D001704:Biopolymers; D002364:Caseins; D004220:Disulfides; D012967:Sodium Dodecyl Sulfate