Functional Implications of Interactions of Extracellular Ions with Ligands of the Cell Membrane

Three examples are discussed in which interactions of chemical agents with ligands of the plasma membrane have been chemically characterized and in which the resulting disturbance in membrane function has been quantitatively measured. Uranyl ion reacts with phosphoryl groups and specifically blocks the transfer of glucose across the membrane. Cationic redox dyes and mercuric chloride react with sulfhydryl groups and destroy the structural integrity of the membrane. Arsenate competes with phosphate for a specific active-transport system and blocks the system by irreversibly combining with one of its components.