The cell membrane establishes critical concentration gradients between the
interior and exterior of cells.
An intracellular to extracellular difference in sodium and potassium ion
concentrations is essential to the function of nerves, transport of important
nutrients into the cell, and maintenance of proper cell volume.
i) Discovery and characterization of the actual molecular pump that establishes
the sodium and potassium concentration gradient (Na+, K+-ATPase) earned
Jens Skou (Aarhus University, Denmark) one half of the 1997 Nobel Prize in
Chemistry. The other half went to Paul D. Boyer (UCLA) and John E.
Walker (Cambridge) for elucidating the enzymatic mechanism of ATP
synthesis.
There is a family of antibiotics (ionophores) whose effectiveness results from
disrupting this crucial ion gradient.
Monesin binds with sodium ions and carries them across the cell membrane and is
called a carrier ionophore.
Other ionophore antibiotics such as gramicidin and valinomycin are
channel-forming ionophores because they open pores that extend through the
membrane.
The ion-transporting ability of monensin results principally from its many ether
functional groups, and it is an example of a polyether antibiotic.
i) The oxygen atoms of these molecules bind with metal ions by Lewis acid-base
interactions.
ii) Each monensin molecule forms an octahedral complex with a sodium ion.
iii) The complex is a hydrophobic “host” for the ion that allows it to be carried as a
“guest” of monensin from one side of the nonpolar cell membrane to the other.
iv) The transport process destroys the critical sodium concentration gradient
