uniportörer

Uniportörer (uniporters) are membrane transport proteins that mediate the passive, facilitated diffusion of a single type of substrate across a biological membrane. Unlike channels, which form pores for ions to diffuse through, uniportörer operate by alternating access: the substrate binds on one side, the protein undergoes a conformational change, and the substrate is released on the other side. The transport proceeds down the substrate’s concentration gradient and does not couple to the movement of other solutes or ions.

Uniportörer are saturable and display specificity for their substrate. Kinetics are described by Michaelis-Menten-like behavior, with a maximal transport rate (Vmax) and an apparent affinity (Km) reflecting transporter density and affinity. Many uniportörer belong to families with multiple substrate specificities, including the glucose transporters (GLUT family) that move glucose across the plasma membrane, and various amino acid or nucleotide transporters. Subcellular localization and regulation—through transcriptional control, trafficking to the membrane, and post-translational modifications—determine transport capacity in tissues.

Defects or altered expression of uniportörer can contribute to disease and metabolic dysregulation. In research, uniportörer are studied to understand nutrient uptake, cellular metabolism, and pharmacokinetics of drugs that resemble endogenous substrates. The term distinguishes these proteins from symporters and antiporters, which move substrates against gradients by coupling to other ions or solutes.