Interaction of two prolamins with 1-13C oleic acid by 13C NMR.

In this paper, we analyzed the interaction of Z19 prolamin from a BR451 maize variety and pennisetin from a BRS1501 pearl millet variety with 1-(13)C-enriched oleic acid (OA) by (13)C NMR in solution. In both proteins, we identified the presence of free fatty acids by NMR in solid state and solution. The interactions were analyzed at the protein/OA molar ratios of 1:1 and 1:4. In the Z19/OA 1:1 mixture in 70% ethanol and 30% D(2)O, the chemical shift of OA C1 was 182.9 ppm, about 3 ppm above that of the pure OA in the same solvent. In contrast, upon addition of OA to the pennisetin (1:1), the chemical-shift value slightly decreased by less than 1 ppm. The chemical-shift titration curve of OA C1 in an apparent pH range of 5.5-7.3 shifted by approximately 0.3 pH units toward higher pH values in the pennisetin/OA 1:1 complex relative to the pure OA. The results obtained for the pennisetin/OA 1:4 mixture were similar to the complexes at a 1:1 molar ratio. A significant difference was observed between the 1:1 and 1:4 curves for Z19. The titration curve for Z19/OA 1:1 suggested specific binding at the sites with electrostatic interaction.