Fractionation of the Protein Components of Human Erythrocyte Membranes

The proteins of the human erythrocyte membrane can be fractionated into several groups. Approximately one-half of the proteins in the membrane can be removed by sequential extraction of the erythrocyte ghost, first with a solution containing chelating agents, and then with concentrated NaCl solutions. A small amount of the membrane proteins (less than 10% of the total proteins) remains in the organic phase during alcohol-ether and ether extraction of the partially fractionated membrane. The remaining membrane proteins can be solubilized in solutions of sodium dodecyl sulfate and fractionated by gel filtration into distinct groups. The amino acid and carbohydrate compositions of the eight fractions thus obtained are presented. Four of the protein fractions have large amounts of sialic acid. Several fractions contain a much greater proportion of nonpolar amino acids than does the membrane as a whole. The number of individual components in each of the fractions has been studied by acrylamide gel electrophoresis and NH2-terminal amino acid analysis. There are at least 12 different membrane proteins present in significant amounts. The size of the membrane proteins varies from about 10,000 to 150,000 in molecular weight.