Reconstitution of the transferrin receptor in lipid vesicles. Effect of cholesterol on the binding of transferrin.

: Purified rabbit reticulocyte transferrin receptors were incorporated into phosphatidylcholine vesicles containing varying amounts of cholesterol. The binding of transferrin to the receptor in the reconstituted vesicles had three distinct characteristics: (1) The binding of transferrin exhibited the two components characteristic of transferrin binding to erythroid cells, a saturable, specific component and a nonsaturable, nonspecific component. (2) Transferrin binding exhibited positive cooperativity at low cholesterol/phospholipid (C/P) molar ratios. However, the cooperativity diminished and then disappeared as the C/P molar ratios were increased to the levels found in circulating red blood cells. (3) The amount of specific transferrin binding to the reconstituted vesicles also decreased as the C/P molar ratio was increased. These results indicate that in the reconstituted system the lipid environment plays a significant role in the expression of transferrin receptors.