CHARACTERIZATION OF PHOSPHATE SITES IN NATIVE OVINE, CAPRINE, AND BOVINE CASEIN MICELLES AND THEIR CASEINOMACROPEPTIDES - A SOLID-STATE P-31 NUCLEAR-MAGNETIC-RESONANCE AND SEQUENCE AND MASS-SPECTROMETRIC STUDY

The phosphate sites in native ovine, caprine, and bovine casein micell es have been analyzed using sequence analysis, mass spectrometric anal ysis, and solid-state P-31 nuclear magnetic resonance spectroscopy. Us ing a combination of S-ethylcysteine derivatization, sequence analysis , and mass spectrometric analysis, the phosphorylation sites of ovine (SerP(151) and SerP(168)), caprine (SerP(151) and SerP(168)), and bovi ne (SerP(149)) caseinomacropeptides have been localized. Various solid -state P-31 methods using magic angle spinning have been applied to as certain the local structure and dynamics of the phosphorylated serine residues and the inorganic calcium phosphates within the micelles. Con tributions from the phosphorylated serine residues of kappa-CN, locate d in the C-terminal portion of the molecule, to the mobile constituent s of the micelles were assigned by comparison with P-31 nuclear magnet ic resonance spectra of purified caseinomacropeptide from the various species in the dissolved state. Comparison of the P-31 magic angle spi nning nuclear magnetic resonance spectra of ovine, caprine, and bovine casein micelles indicates that the micelles from these species are ve ry similar but not identical.