The inositol hexaphosphate (IHP) method for purification of the erythrocyte membrane protein 4.1 yields the largest quantity of pure protein of any published protocol. However, protein 4.1 isolated by this method was found to bind to KI-stripped inside-out red blood cell membrane vesicles (KIOVs) only 40% as well as protein 4.1 purified by other methods. While an improved Tyler method, the SP method, yields 30-40% less protein 4.1 than the IHP method, the SP preparation nevertheless exceeds the IHP method in that the protein 4.1 is fully functional. Unlike the Tyler method, the SP procedure is also free of contaminating spectrin, p55, and proteases.
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