The IUBMB-Endorsed Transporter Classification System

Transport systems are essential to every living cell. They (1) allow the entry of all essential nutrients into the cell and its compartments, (2) regulate the cytoplasmic concentrations of metabolites by excretion mechanisms, (3) provide physiological cellular concentrations of ions that can differ by several orders of magnitude from those in the external medium, (4) export macromolecules such as complex carbohydrates, proteins, lipids, and DNA, (5) catalyze export and uptake of signaling molecules that mediate intercellular communications, (6) prevent toxic effects of drugs and toxins by mediating active efflux, and (7) participate in biological warfare by exporting biological active agents that insert into or permeate the membranes of target cells. Transport is an essential aspect of all life-endowing processes: metabolism, communication, biosynthesis, reproduction, and both cooperative and antagonistic interorganismal behaviors.