Ionophores are compounds which can facilitate the migration of ions across biological membranes. Ions, being electrically charged, cannot by themselves cross the hydrophobic interior of biological membranes.

Ionophores usually have a polar inner moiety, and a non-polar outer moiety which can span or cross the hydrophobic interior of the membrane. Ionophore function usually affects metallic cations.

There are two types of ionophores: Channel-formers and Carriers. Channel formers are usually large proteins. They usually function by incorporating themselves into the cell-membrane, creating a polar “tube” across the membrane, enabling ions pass through. Carriers are usually smaller molecules, with a non-polar exterior and a polar interior.

The polar interior can reversibly bind an ion, effectively wrapping the electric charge of the ion within a non-polar envelope. The non-polar envelope can then cross the interior of the membrane, carrying the ion with it.

Ionophores can interfere with the balance of ion concentrations across membranes. Maintenance of ionic gradients across the cell membrane is an essential biological function. In interfering with such ionic gradients, ionophores often display antibiotic properties. Several novel works have been published, where natural ionophore compounds, when fed to cattle in liquid, solid or medicinal form, increased calf weight gain in correlation to the amount given.