Antiport

The gradients of H, Na, and other cations and anions established by ATPases and other energy sources can be used for secondary active transport of various substrates. The best-understood systems use Na or gradients to transport amino acids and sugars in certain cells. Many of these systems operate as symports, with the ion and the transported amino acid or sugar moving in the same direction (that is, into the cell). In antiport processes, the ion and the other transported species move in opposite directions. (For example, the anion transporter of erythrocytes is an antiport.) Proton symport proteins are used by E. coU and other bacteria to accumulate lactose, arabinose, ribose, and a variety of amino acids. E. coli also possesses Na -symport systems for melibiose as well as for glutamate and other amino acids. 

Sodium calcium exchanger Na+/Ca2+ exchanger Na+/Ca2+ antiporter NCX NCX1 NCX2 NCX3... 

The site level at which [Ca2+]i regulates NCX activity (CBD) is different from the one required for Ca2+ transport. Submicromolar concentrations (0.1-0.3 pM) of intracellular Ca2+ are needed to activate the antiporter through these Ca2+ binding site. The location of such regulatory site has been identified in the 134-amino acid-length region, situated in the center of the intracellular f loop [2], (Table 1)... 

Among the organic derivates, amiloride analogs were the first to be described as powerful inhibitors of NCX activity when the antiporter operates either in the forward or the reverse mode of operation (Fig. 5). These... 

Very recently, the further screening of new benzy-loxyphenyl derivatives revealed a highly potent NCX inhibitor, named YM-244769. This orally bioavailable compound is more potent inhibiting NCX3 than NCX1 and NCX2 in the reverse mode, but it is not active on the forward mode of operation of the three antiporter isofoims. (Table 4)... 

Sodium-proton exchanger Sodium-proton antiport... 

Sialin was first identified as the product of the gene defective in sialidosis, a lysosomal storage disorder. The transporter mediates the movement of sialic acid out of lysosomes by coupling to the proton electrochemical gradient across the lysosomal membrane. Unlike the vesicular neurotransmitter transporters which are antiporters, sialin is a sympoiter with sialic acid and protons both moving out of the lysosome. 

Electrogenic antiport, ADP uptake favored by the membrane potential can also mediate electroneutral exchange of ADPout for... 

Elecironeutral symport, has also been formulated as Pp70H antiport... 

Electroneutral antiport Electroneutral antiport Electroneutral antiport... 

Electrogenic antiport, can only operate in the direction of aspartate efflux as import of H is a requirement for the malate/aspartate shuttle... 

Presumably can exchange acyl-carnitineoui or acyl-carnitineifs, or carnitineoui carnitineiN Electroneutral antiport... 

Blumwald, E. Poole, R.J. (1987). Salt tolerance in suspension cultures of sugar beet. Induction of Na /H" antiport activity at the tonoplasts by growth and salt. Plant Physiology, 83, 884-7. 

Figure 12-11. Combination of phosphate transporter ( ) with the adenine nucleotide transporter ((2)) in ATP synthesis. The H+ZP, symport shown is equivalent to the P /OH antiport shown in Figure 12-10. Four protons are taken into the mitochondrion for each ATP exported. However, one less proton would be taken in when ATP is used inside the mitochondrion.

Transport systems can be described in a functional sense according to the number of molecules moved and the direction of movement (Figure 41-10) or according to whether movement is toward or away from equilibrium. A uniport system moves one type of molecule bidirectionally. In cotransport systems, the transfer of one solute depends upon the stoichiometric simultaneous or sequential transfer of another solute. A symport moves these solutes in the same direction. Examples are the proton-sugar transporter in bacteria and the Na+ -sugar transporters (for glucose and certain other sugars) and Na -amino acid transporters in mammalian cells. Antiport systems move two molecules in opposite directions (eg, Na in and Ca out). 

In Oxalobacter formigenes, oxalate and its decarboxylation product formate form a one-to-one antiport system, which involves the consumption of an internal proton during decarboxylation, and serves as a proton pump to generate ATP by decarboxylative phosphorylation (Anantharam et al. 1989). 

Iyer R, C Williams, C Miller (2003) Arginine-agmatine antiporter in extreme acid resistance in Escherichia coli. J Bacterial 185 6556-6561. 

Ruan Z-S, V Anantharam, IT Crawford, SV Ambudkar, SY Rhee, MY Allison, PC Maloney (1992) Identification, purification, and reconstitution of OxlT, the oxalate formate antiport protein of Oxalobacter formigenes. J Biol Chem 267 10537-10543. 

Ionization may be used to counteract disregulation of pH levels (which is maintained through the concerted action of Na /H antiporters, CL/HCO3" exchangers, and other channels and/or transporters that exist within the plasma membrane of eucaryotic cells [32,100,101]). Indeed, it has been shown that iono-phores (such as nigericin [102]) can lower the intracellular pH, while weak acids (such as propionic acid) can promote acidification. Likewise, nonsteroidal anti-... 

The difference in the hydrogen ion electrochemical potential, formed in bacteria similarly as in mitochondria, can be used not only for synthesis of ATP but also for the electrogenic (connected with net charge transfer) symport of sugars and amino acids, for the electroneutral symport of some anions and for the sodium ion/hydrogen ion antiport, which, for example, maintains a low Na+ activity in the cells of the bacterium Escherichia coli. 

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