RED-CELL MEMBRANE-PROTEIN ANOMALIES IN CONGENITAL DYSERYTHROPOIETIC ANEMIA, TYPE-II (HEMPAS)

In all of 6 cases of congenital dyserythropoietic anemia, type II (HEMPAS), gel electrophoresis in the presence of SDS [sodium dodecyl sulfate] revealed abnormally rapid migration of the preponderant integral membrane protein, band 3. After proteolysis of intact cells, the remaining part of the band 3, comprising the intramembrane segment and the cytoplasmic domain, migrated electrophoretically as a single band, identical in mobility to that from normal cells treated in the same manner. The anomaly thus resided in the extracellular domain of the protein, which is the glycosylated part of the chain. Peptide digests of the band 3 showed no evidence of a missing protein segment in the abnormal cells and the amino acid composition of the peptides derived from proteolysis of the extracellular protein of intact cells was also normal. The anomaly is apparently one of glycosylation. The major glycoproteins, detected by carbohydrate-specific (PAS [periodic acid Schiff]) stain appeared normal in SDS gels. When the more sensitive procedure of reacting after electrophoresis with radioiodinated lentil lectin is employed, some additional minor protein components were revealed. One species of apparent subunit MW .apprx. 150,000 appeared in all cases of HEMPAS examined and in no normals. This component is not accessible to proteolysis by chymotrypsin or Streptomyces griseus protease and may be associated with the inner membrane patches, characteristic of the HEMPAS condition. Overall cell shape and microviscosity of the membrane bilayer, as measured by fluorescence polarization of a lipid-soluble fluorophore, were substantially normal in HEMPAS cells.