Reaction of dimethyl-3,3'-dithiobispropionimidate with intact human erythrocytes. Cross-linking of membrane proteins and hemoglobin.

Dimethyl-3,3'-dithiobispropionimidate penetrates intact human erythrocytes and cross-links many of the membrane proteins to hemoglobin as well as to each other. The cross-linked complexes so produced have been analyzed by both one- and two-dimensional sodium dodecyl sulfate polyacrylamide gel electrophoresis, making use of the easy cleavability of the disulfide-containing reagent. The basic pattern of cross-linked complexes appears identical with that seen with unsealed ghosts. Although subtle relative motions cannot be ruled out, no rearrangement of nearest neighbor peptide chains, on a scale that would alter the cross-linking pattern, occurs during osmotic lysis of erythrocytes. Superimposed on the basic pattern was a series of complexes involving globin chains. Bands 1, 2, 2.2, 2.4, 3, 4.1, 4.2, 6, and 7 (nomenclature of Steck, T.L. (1972) J. Mol. Biol. 66, 295-305) are all cross-linked to hemoglobin. Bands 2.2 and 2.4, recently shown to be accessible to the external surface of the membrane (Staros, J. V., and Richards, F. M. (1974) Biochemistry 13, 2720-2726), may be transmembrane proteins on the basis of the present findings. Band 5 is the only major band to show no detectable complexes with hemoglobin; oligomers of Band 5 itself, however, are seen. The absence of hemoglobin/Band 5 cross-linking in this case could reflect a special, as yet unexplained, environment for the Band 5 peptide. The amount of Band 6 in isolated membranes diminishes with increasing reagent concentration.