Small amount of concanavalin A modifies radiation-induced alteration in cell-surface charge depending on its binding condition

Abstract

Cell electrophoretic mobility of cultured melanoma cells or rat erythrocytes decreased with time after X-irradiation. Addition of tetravalent concanavalin A or divalent succinyl-concanavalin A before (not after) irradiation, completely blocked the mobility reduction in greater concentrations than 5 mug/l. At 5 mug/l only 3.7 - 10(3) concanavalin A molecules bound to receptors per cell, while 4.18 - 10(7) molecules/cell bound at saturating concentrations. Preincubation with concanavalin A at 37 degrees C was effective even when the cells were treated with alpha-methylmannoside immediately after irradiation. At low temperature, however, concanavalin A was not effective despite a sufficient amount of bound 125I-labelled concanavalin A. Treatment with alpha-methylmannoside following the binding of concanavalin A at 37 degrees C before irradiation inhibited the concanavalin A effect depending on temperature. The residual amount of bound lectin could not account for the temperature dependence. The amount of sialic acid (the main charged substance) was not altered by X-irradiation with or without the lectin. Divalent succinyl-concanavalin A was also effective in blocking the radiation effect on electrophoretic mobility. These results seem to suggest that binding of a very small amount of concanavalin A without causing cell agglutination or clustering of its receptors, induces some alteration in the conformation of receptor glycoprotein, which blocks the internalization of acidic sugar residues by subsequent irradiation.