Reconstituted micelle formation using reduced, carboxymethylated bovine kappa-casein and human beta-casein.
In milk, kappa-casein, a mixture of disulfide-bonded polymers, stabilizes and regulates the size of the unique colloidal complex of protein, Ca2+ and inorganic phosphate (Pi) termed the casein (CN) micelle. However, reduced, carboxymethylated bovine kappa-CN (RCM-kappa) forms fibrils at 37 degrees C and its micelle-forming ability is in question. Here, the doubly- and quadruply-phosphorylated human beta-CN forms and 1:1 (wt:wt) mixtures were combined with RCM-kappa at different beta/kappa weight ratios. Turbidity (OD(400 nm)) and a lack of precipitation up to 37 degrees C were used as an index of micelle formation. Studies were with 0, 5 and 10 mM Ca2+ and 4 and 8 mM Pi. The RCM-kappa does form concentration-dependent micelles. Also, beta-CN phosphorylation level influences micelle formation. Complexes were low-temperature reversible and RCM-kappa fibrils were seen. There appears to be equilibrium between fibrillar and soluble forms since the solution still stabilized after fibril removal. The RCM-kappa stabilized better than native bovine kappa-CN.
Sood
Satish M
SM
Department of Biochemistry and Microbiology, Biochemistry Division School of Medicine,, Loma Linda University, Loma Linda, CA 92350, USA. ssood@llu.edu
Lekic
Tim
T
Jhawar
Harbir
H
Farrell
Harold M
HM
Slattery
Charles W
CW
D000682:Amyloid / Q000096:biosynthesis; D000818:Animals; D002118:Calcium / Q000494:pharmacology; D002364:Caseins / Q000737:chemistry* / Q000378:metabolism; D002417:Cattle; D002614:Chelating Agents / Q000737:chemistry* / Q000378:metabolism; D006801:Humans; D008745:Methylation; D008823:Micelles; D009391:Nephelometry and Turbidimetry; D010084:Oxidation-Reduction; D013696:Temperature
D000682:Amyloid; D002364:Caseins; D002614:Chelating Agents; D008823:Micelles; D002118:Calcium