permease

Permease is a membrane transport protein that facilitates the movement of specific solutes across biological membranes. Permeases are integral membrane proteins that mediate uptake or efflux of nutrients, metabolites, and waste products, usually by coupling transport to an existing electrochemical gradient or by providing a substrate-specific passage.

They function in facilitated diffusion (as uniporters or symporters) or active transport (using energy from proton motive force or ion gradients). They differ from channels in that they typically undergo conformational changes to move substrates and display saturable kinetics. Common modes include symport, antiport, and unidirectional transport.

Most permeases belong to multi-pass transmembrane protein families, such as the Major Facilitator Superfamily (MFS). Many bacterial and eukaryotic permeases have around 10-14 transmembrane helices arranged in two domains. A well-known example is lactose permease LacY of Escherichia coli, which imports lactose in symport with H+.

Permeases enable uptake of sugars, amino acids, phosphate, and other nutrients; in some organisms, permeases contribute to drug uptake or antibiotic susceptibility. Permeases are often encoded in operons or gene families and regulated by substrate availability or environmental conditions.

See also: transporter, facilitated diffusion, active transport.