Wang Q, Allen J C, Swaisgood H E
Department of Food Science, North Carolina State University, Raleigh 27695-7624, USA.
J Dairy Sci. 1997 Jun;80(6):1054-9. doi: 10.3168/jds.S0022-0302(97)76030-2.
beta-Lactoglobulin was isolated directly from acidic whey by bioselective adsorption on N-retinyl-Celite, yielding preparations of > or = 96% purity. Interactions of these preparations with vitamin D2, vitamin D3, ergosterol, cholesterol, and 7-dehydrocholesterol were examined by following changes in the fluorescence spectra. Both the excitation and emission spectra indicated that energy was transferred between the tryptophanyl residues of the protein and the chromophore of the ligand. Analyses of the fluorescence changes that occurred upon titration of beta-LG with the various ligands allowed determination of the dissociation constant for the complex and the number of moles bound per mole of protein. The affinity for vitamin D2 (dissociation constant of 4.91 nM) was 10-fold higher than that of the other compounds, except for ergosterol, which was 5-fold larger than the others. Also, the affinity was 10-fold higher than that typically reported for the retinoids. Furthermore, the value obtained for the number of moles bound per mole of protein was 2 mol.mol-1 for each of the ligands examined in this study; it has been well established that all of the retinoids are bound with a stoichiometry of 1.0. These results suggest that beta-LG may be a better carrier of vitamin D than of vitamin A.
通过在N-视黄基-硅藻土上进行生物选择性吸附，直接从酸性乳清中分离出β-乳球蛋白，得到纯度≥96%的制剂。通过跟踪荧光光谱的变化，研究了这些制剂与维生素D2、维生素D3、麦角固醇、胆固醇和7-脱氢胆固醇的相互作用。激发光谱和发射光谱均表明，能量在蛋白质的色氨酸残基和配体的发色团之间转移。通过用各种配体滴定β-LG时发生的荧光变化分析，可以确定复合物的解离常数和每摩尔蛋白质结合的摩尔数。对维生素D2的亲和力（解离常数为4.91 nM）比其他化合物高10倍，但麦角固醇除外，其比其他化合物高5倍。此外，该亲和力比通常报道的类视黄醇高10倍。此外，本研究中检测的每种配体每摩尔蛋白质结合的摩尔数为2 mol·mol-1；已经确定所有类视黄醇的化学计量比为1.0。这些结果表明，β-LG可能是维生素D比维生素A更好的载体。
