Cross-Linking of Membrane Proteins of Metabolically-Depleted and Calcium-Loaded Erythrocytes

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Abstract
Membranes of [human] erythrocytes undergoing metabolic depletion or an influx of Ca undergo several changes in structure and function. In erythrocytes incubated without substrate extensive cross-linking of membrane proteins by disulfide bonding was found occurring after 24-48 h, involving all major membrane proteins including Hb. Aggregates of MW 40 .times. 106 or greater were formed. These changes were partially reversible by repletion with adenosine. Rapid introduction of Ca (intracellular concentrations approximately 0.6 mM) into metabolically replete erythrocytes with the ionophore A23187 results in transglutaminase dependent cross-linking of membrane proteins. Cellular Ca concentrations of approximately 0.3 mM have no cross-linking effect. Cells undergoing metabolic depletion show progressive loss of transglutaminase activity to undetectable levels at 12 h, so that influx of Ca into such cells cannot cause cross-linking by a transglutaminase mediated reaction. The metabolic state of the cell and the rate and degree of Ca influx into erythrocytes were critical factors in determining the type of membrane protein cross-linkage.