Porter antiporter symporter

Many active-transport systems couple the uphill flow of one ion or molecule to the downhill flow of another. These membrane proteins, called secondary transporters or cotransporters, can be classified as antiporters, symporters, and uni porters. Antiporters couple the downhill flow of one type of ion in one direction to the uphill flow of another in the opposite direction. Symporters move both ions in the same direction. Uniporters transport a substrate in either direction, determined by the concentration differences. Studies of the lactose permease from E. coli have been a source of insight into both the structures and the mechanisms of secondary transporters. 

A. Porters uniporters, symporters, and antiporters 2.A.I. Major facilitator superfamily (MFS)... 

Na -glucose symporter in epithelial cells 2.A.73. HCOs transporters HCOs-CI" antiporter 2.B. Nonribosomally synthesized porters 2.B.I. Valinomycin carrier family Valinomycin... 

In the Organophosphate Phosphate Antiporter (OPA) family (2. A. 1.4), most members preferentially catalyze substrate substrate antiport, but they can also catalyze substrate H symport, and some preferentially seem to use a symport rather than an antiport mechanism. Also, in the Nitrate/ Nitrite Porter (NNP) family (2.A. 1.8), members of similar sequence can catalyze either uptake, efflux, or NO j NO exchange. Finally, members of the Organocation Transporter (OCT) family in animals (2.A.1.19) appear to be mechanistically promiscuous, catalyzing substrate uptake, export, exchange, and/or uniport. Sometimes the mechanism and substrate H stoichiometry depends on... 

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