Bovine β-lactoglobulin (BLG) in vivo has been
found complexed with fatty acids, especially palmitic and
oleic acid. To elucidate the still unknown structure-function
relationship in this protein, the interactions between
13C enriched palmitic acid (PA) and BLG were
investigated by means of one-, two-, and three-dimensional
NMR spectroscopy in the pH range 8.4–2.1. The NMR
spectra revealed that at neutral pH the ligand is bound
within the central cavity of BLG, with the methyl end deeply
buried within the protein. The analysis of 13C
spectra of the holo protein revealed the presence of conformational
variability of bound PA carboxyl end in the pH range 8.4–5.9,
related to the Tanford transition. The release of PA starts
at pH lower than 6.0, and it is nearly complete at acidic
pH. This finding is relevant in relation to the widely
reported hypothesis that this protein can act as a transporter
through the acidic gastric tract. Ligand binding and release
is shown to be completely reversible over the entire pH
range examined, differently from other fatty acid binding
proteins whose behavior is analyzed throughout the paper.
The mode of interaction of BLG is compatible with the proposed
function of facilitating the digestion of milk fat during
the neonatal period of calves.