BINDING AFFINITIES OF BETA-IONONE AND RELATED FLAVOR COMPOUNDS TO BETA-LACTOGLOBULIN - EFFECTS OF CHEMICAL MODIFICATIONS

The effects of chemical modifications, esterification or reductive alkylation, on binding properties of several terpenes by β-lactoglobulin were examined. As shown by fluorescence quenching, β-lactoglobulin and its derivatives bind β-ionone, but it does not bind α-ionone, neither geraniol nor R(+)- and S(-)-limonene. It is suggested that its binding site, presumably situated within the calyx-shaped protein fold (North, A. C. T. Int. J. Biol. Macromol. 1989,11, 56–58), has a narrow specificity to the structure formed by the conjugated double bonds of the β-ionone ring and isoprenoid chain, present in both ter penes—(3-ionone and retinol. The complexes of β-ionone with the derivatives of β-lactoglobulin (except N-ethyllysyl-BLG) exhibit lower Kd' values than that of the complex of β-ionone with unmodified β-lac toglobulin. N-Methyllysyl-BLG and EtBLG are binding β-ionone stronger than the other even more extensively modified derivatives as, for example, N-ethyllysyl-BLG and MetBLG. The partial loss of BLG β-barrel structure achieved during extensive esterification producing MetBLG, deduced from the analysis of circular dichroism spectra, could explain its less effective binding to β-ionone. © 1990, American Chemical Society. All rights reserved.