Interaction of α-lactalbumin with phospholipid vesicles

Abstract

$\alpha$-Lactalbumin binding to large-volume vesicles are investigated by a technique based on the separation by centrifugation of phospholipid-bound protein from the bulk solution. Large-volume vesicles are prepared by using the ether injection method and they appeared to be unilamellar judging from their electron micrograms. Interaction of $\alpha$-lactalbumin with the vesicles are carried out in 10mM TRIS buffer solution (pH 7.0) at various NaCl concentrations. The experimental temperature is maintained at $4\,^\circ\!C$. The results show that $\alpha$-lactalbumin binds only to vesicles containing stearylamine, and that the vesicle seems to have a limited number of independent binding sites. The dissociation constants are calculated from the double-reciprocal plots of concentrations of bound and free proteins. The results also show that the dissociation constants increase with increasing ionic strength, and with decreasing stearylamine content in the vesicles. This result suggests that the interaction between $\alpha$-lactalbumin and phospholipid vesicles is primarily electrostatic in nature.