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

Summary. The membranes of erythrocytes undergoing metabolic depletion or an influx of calcium undergo several changes in structure and function. In erythrocytes incubated without substrate we find extensive cross‐linking of membrane proteins by disulphide bonding occurring after 24–48 h, involving all major membrane proteins as well as haemoglobin. Aggregates of mol wt 40 × 106 or greater are formed. These changes are partially reversible by repletion with adenosine. Rapid introduction of calcium (intracellular concentrations approximately 0.6 mm) into metabolically replete erythrocytes with the ionophore A23187 results in transgluta‐minase‐dependent cross‐linking of membrane proteins. Cellular calcium concentrations of approximately 0.3 mm have no cross‐linking effect. Cells undergoing metabolic depletion show a progressive loss of transglutaminase activity to undetec‐table levels at 12 h, so that influx of calcium into such cells cannot cause cross‐linking by a transglutaminase‐mediated reaction. These studies suggest that the metabolic state of the cell and the rate and degree of calcium influx into erythrocytes are critical factors in determining the type of membrane protein cross‐linkage.