Binding capacity of alpha-crystallin to bovine lens lipids.

Three experiments were performed to determine the alpha-crystallin binding capacity of bovine lens lipid vesicles. In one experiment lipid was kept constant (2.5 mg ml-1) and the alpha-crystallin concentration was changed (0.5 to 3.0 mg ml-1). In another experiment, alpha-crystallin was kept constant (1 mg ml-1) and the concentration of lipid was varied (0.25 to 3 mg ml-1). We calculated the binding capacity of the lipid to be 0.33 +/- 0.05 (S.D.) mg alpha-crystallin (mg lens lipid)-1. This was confirmed by changes in the anisotropy and fluorescent intensity of a probe that partitions at the headgroup region of the lipid bilayer. Near 0.33 mg alpha-crystallin (mg lens lipid)-1 the fluorescence intensity and anisotropy of the probe increases and plateaus which indicates that concomitant with alpha-crystallin binding, water is excluded from the head group region of the bilayer and the headgroup region becomes less mobile. It is possible that alpha-crystallin binding could protect and stabilize the lipid bilayer and decrease membrane permeability.