Membrane transport protein

Definition

A membrane transport protein is a special kind of transmembrane protein associated with a biological membrane that facilitates the movement of one or more of these across the membrane: ions, small molecules, or macromolecules (such as other proteins). Note that a specific membrane transport protein may facilitate the movement of only a few specific ions across the biological membrane.

Relation with other terminology

Broader terminology

• Membrane transport proteins associated with a biological membrane are transmembrane proteins for that biological membrane. Concretely, transmembrane proteins are proteins permanently attached to both layers of the lipid bilayer that the membrane is made up of. A membrane transport protein must be a transmembrane protein since it needs to be on both sides in order to facilitate movement from one side to another.
• Transmembrane proteins are, in turn, instances of integral membrane proteins, i.e., proteins permanently attached to a biological membrane.
• Integral membrane proteins are, in turn, instances of membrane proteins, i.e., proteins that interact with a biological membrane.

More specific terminology

• Solute carrier refers to a particular kind of membrane transport protein that has a specific direction of transport for each ion or molecule that it transports (these directions may be opposite to each other for different things being transported, as seen for antiporters). In general, the term "carrier" is used for facilitating movement in one specific direction.
• Ion channel refers to a particular kind of membrane transport protein that facilitates the bidirectional movement of ions across the membrane. In general, the term "channel" is used for facilitating bidirectional movement.