Water transport across red-cell membranes following reductive methylation of the major transmembrane protein, band 3: Implications to increased divalent cation membrane permeability

H-T-NMR methods in conjunction with normally membrane-impermeable Mn²⁺ were used to study the effect of reductive methylation of specific lysine residues of Band 3, the major transmembrane protein, on water permeability. At 21°C, the water apparent transverse relaxation time (T₂) was decreased by nearly 16% (p < 00001) for cells with modified Band 3. Atomic absorption measurements of control and methylated cells showed an increased level of Mn²⁺ in the erythrocyte cytosol following methylation. This increased level of this paramagnetic relaxation agent is sufficient to relax interior water protein to the values obtained. Thus, following specific methylation of band 3, increased membrane permeability to divalent cations is observed. The results are discussed with reference to possible conformation changes of Band 3 following methylation, and the findings are interpreted be mean that the conformation of Band 3 has influence on cation permeability to erythrocyte membranes.