Characterization of Phosphate Sites in Native Ovine, Caprine, and Bovine Casein Micelles and Their Caseinomacropeptides: A Solid-State Phosphorus-31 Nuclear Magnetic Resonance and Sequence and Mass Spectrometric Study

¹ University of Aarhus, DK-8000 Aarhus, Denmark

The phosphate sites in native ovine, caprine, and bovine casein micelles have been analyzed using sequence analysis, mass spectrometric analysis, and solid-state ³¹P nuclear magnetic resonance spectroscopy. Using a combination of S-ethylcysteine derivatization, sequence analysis, and mass spectrometric analysis, the phosphorylation sites of ovine (SerP₁₅₁ and SerP₁₆₈) caprine (SerP₁₅₁ and SerP₁₆₈), and bovine (SerP₁₄₉) caseinomacropeptides have been localized. Various solid-state ³¹P methods using magic angle spinning have been applied to ascertain the local structure and dynamics of the phosphorylated serine residues and the inorganic calcium phosphates within the micelles. Contributions from the phosphorylated serine residues of -CN, located in the C-terminal portion of the molecule, to the mobile constituents of the micelles were assigned by comparison with ³¹P nuclear magnetic resonance spectra of purified caseinomacropeptides from the various species in the dissolved state. Comparison of the ³¹P magic angle spinning nuclear magnetic resonance spectra of ovine, caprine, and bovine casein micelles indicates that the micelles from these species are very similar but not identical.

Key Words: magic angle spinning nuclear magnetic resonance • casein micelles • phosphorylation • -casein

Submitted on December 5, 1995
Accepted on September 6, 1996

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