Related Experiment Video
Updated: Jul 10, 2026
11:37
Sigma's Non-specific Protease Activity Assay - Casein as a Substrate
Published on: September 17, 2008
Isolation and Identification of beta-Casein A(1)-4P and beta-Casein A(2)-4P in Commercial Caseinates
1Department of Food Science and Nutrition, University of Minnesota, St. Paul, Minnesota 55108.
Journal of Agricultural and Food Chemistry
|February 7, 2001
Summary
Modified beta-casein (beta-CN) fractions with four phosphate groups were identified in caseinate. These dephosphorylated forms likely result from hydrolysis, differing from alkali-induced beta-elimination.
Area of Science:
- Biochemistry
- Food Chemistry
Background:
- Caseinate, a milk protein derivative, contains various beta-casein (beta-CN) forms.
- Native beta-CN in milk is typically phosphorylated.
Purpose of the Study:
- To characterize modified beta-CN fractions found in different types of caseinate.
- To determine the extent and mechanism of beta-CN dephosphorylation in caseinate.
Main Methods:
- Mass spectrometry was used to determine the molecular weights of beta-CN fractions.
- Phosphorus-31 Nuclear Magnetic Resonance ((31)P NMR) was employed to analyze phosphorylation levels.
Main Results:
- Two modified beta-CN fractions, beta-CN A(1)-4P and beta-CN A(2)-4P, were identified, comprising 5-27% of total beta-CN.
- These modified fractions showed a molecular weight approximately 80 Da less than native beta-CN, indicating the loss of one phosphate group.
- (31)P NMR confirmed the presence of four phosphorylated serine residues in modified fractions, compared to five in native beta-CN.
Conclusions:
- The modified beta-CN fractions are likely beta-CN A(1)-4P and beta-CN A(2)-4P, resulting from the dephosphorylation of native beta-CN A(1)-5P and beta-CN A(2)-5P.
- The dephosphorylation mechanism appears to be enzyme, acid, or alkali hydrolysis, distinct from beta-elimination.
