Binding of Lipophilic Nutrients to ß-Lactoglobulin Prepared by Bioselective Adsorption

¹ Southeast Dairy Foods Research Center, Department of Food Science, North Carolina State University, Raleigh, 27695-7624

The binding of the lipophilic nutrients, retinal, vitamin D₂, and retinyl palmitate by ß-lactoglobulin was measured by analysis of changes in the fluorescence of the tryptophanyl residue of ß-lactoglobulin or the retinyl moiety. The fluorescence intensity of the tryptophanyl residue was quenched by retinoid or vitamin D binding but was enhanced by palmitate binding. The analysis of competitive binding experiments with palmitate indicated that retinal and palmitate did not compete for the same site; however, vitamin D₂, which binds with a stoichiometry of 2, appeared to displace palmitate at higher concentrations. Also, the retinoids and vitamin D₂ were bound more tightly than was palmitate. The results are consistent with the model in which the retinoids and vitamin D₂ bind in the calyx formed by the ß-barrel; palmitate and a second molecule of vitamin D₂ bind in a surface pocket near the dimer contact region. Retinyl palmitate, which has both moieties, appeared to bind at both sites.

Key Words: binding lipophilic nutrients • ßbeta;-lactoglobulin • bioselective adsorption

Submitted on June 1, 1998
Accepted on September 23, 1998

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