Structural membrane proteins were studied from erythrocytes (RBC) of a patient with a nonhemolytic form of hereditary elliptocytosis (HE) who developed a microcytic anemia with fragmented RBC while cobalamin (B12) deficient. Evidence is presented for qualitative changes in the patient's RBC membranes not related to a loss of structural proteins. Sensitivity of RBC to heat treatment was studied as well as quantitative changes in proteins by densitometry of 1% SDS--10% PAGE gels. Fractions of RBC of various sizes from the patient while B12 deficient all possessed a marked degree of heat sensitivity when compared to RBC from the patient after B12 repletion, normal family members, HE controls, B12-deficient controls, anemic controls, and normal controls. Because loss of spectrin (bands 1 + 2) from heat- sensitive RBC membranes in hereditary pyropoikilocytosis has been reported, the amount of spectrin relative to band 3 was measured. No decrease in the ratio of bands (1 + 2)/3 was found. In addition, no chromatographically abnormal membrane proteins were found by SDS-PAGE of the patient's RBC while B12 deficient. Our findings indicate that B12 deficiency results in an abnormal membrane with enhanced instability in some forms of HE. Since protein loss was not found, we conclude that an alteration in membrane protein interaction may be involved.

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