Laser photo-CIDNP detection of surface aromatic residues in dissociating bovine alpha-lactalbumin at submillimolar concentrations.

Surface aromatic residues of bovine alpha-lactalbumin were detected by laser photo-CIDNP NMR spectroscopy in the submillimolar (100 micro M) range. The association behavior of this protein was observed in this range (Kd approximately equal to 100 micro M) by the variation in absolute NMR peak intensities for surface polarized residues as the monomer-monomer association step lowered surface residue accessibilities. This example was also the first case reported for laser photo-CIDNP studies of proteins where all three polarizable aromatic residues (tyrosine, tryptophan, and histidine) were observed.