The major "intrinsic" membrane protein of human erythrocytes. Preparative isolation and immunoelectrophoretic analyses.

(1) Preparative dodecyl sulfate gel electrophoresis of human erythrocyte membrane proteins has been used to isolate dodecylsulfate band 3 containing the M,N-glycoprotein and the major "intrinsic" membrane protein (Fairbanks, G., Steck, T.L. and Wallach, D.F.H. (1971) Biochemistry 10, 2606-2617; Bretscher, M.S. (1971) J. Mol. Biol. 59,351-357; Bretscher, M.S. (1971) Nat. New Biol. 231, 229-232 and Marchesi, V.T. and Andrews, E.P. (1972) Science 174, 1247-1248). Subsequent isoelectric focusing in polyacrylamide gels containing Triton X-100 separates these two entities and allows their simultaneous purification. (2) The proteins thus obtained retain their antigenic properties. They are pure according to electrophoretic and immunoelectrophoretic criteria. However, crossed immunoelectrophoresis yields evidence for molecular microheterogeneity of the major "intrinsic" protein. (3) Analyses utilizing crossed immunoelectrophoresis with antibodies absorbed with intact erythrocytes show that the major "intrinsic" protein possesses antigenic determinants on both membrane surfaces and therefore spans the erythrocyte membrane. All determinants of the M,N-glycoprotein detectable with our antibodies were found solely on the exterior membrane surface. (4) Neither the major "intrinsic" membrane protein nor the major M,N-glycoprotein bound significantly to concanavalin A in crossed immunoaffinoelectrophoresis.