Influence of competitive adsorption of a lysopalmitoylphosphatidylcholine on the functional properties of puroindoline, a lipid-binding protein isolated from wheat flour

The functional properties of a low molecular weight lipid-binding protein, puroindoline from wheat, were studied as a function of lysophosphatidylcholine (LPC) concentration. Puroindoline bound approximately five LPC molecules in a positively cooperative manner with a dissociation constant of 54.3 micromolars. The foaming properties of puroindoline were enhanced in mixtures containing LPC, and maximum stability was observed in the range of LPC to puroindoline molar ratios (R) of 1-10. The properties of isolated foam lamellae (thin films) were investigated to explain this observation. Film drainage, equilibrium thickness, surface diffusion in the adsorbed layer by fluorescence recovery after photobleaching, and surface displacement measurements were made. We conclude that the foaming properties of this highly foam active protein are enhanced by addition of LPC, probably by formation of a complex, which reduces puroindoline aggregation at the interface. However, foam stability begins to decrease once there is enough LPC present in the system to allow the protein to diffuse laterally in the adsorbed layer.