Membrane transport antiport

Tamai, L, Takanaga, H., Maeda, H., Yabuuchi, H., Sai, Y., Suzuki, Y., and Tsuji, A., Intestinal brush-border membrane transport of monocarboxylic acids mediated by proton-coupled transport and anion antiport mechanisms, J. Pharm. Pharmacol, 49, 108, 1997. 

Figure 3.7 Membrane transporters involved in active transport. (A) a uniport, (B) a symport, and (C) an antiport.

The interconversion of o -ketoglutarate to glutamate involves the malate-aspartate shutde. This shuttle translocates a-ketoglutarate from mitochondria into the cytoplasm and then converts it to glutamate by the catalytic action of aspartate aminotransferase (McKenna et al., 2006). As part of the malate-aspartate shuttle, NADH is oxidized during reduction of oxaloacetate to malate. Malate diffuses across the outer mitochondrial membrane (Fig. 1.6). From the intermembrane space, the malate-a-ketoglutarate antiporter in the inner membrane transports malate into the matrix. For every malate molecule entering the matrix compartment, one molecule of... 

A FIGURE 8-10 The malate shuttle. This cyclical series of reactions transfers electrons from NADH in the cytosol (intermembrane space) across the inner mitochondrial membrane, which is impermeable to NADH itself. StepH Cytosolic malate dehydrogenase transfers electrons from cytosolic NADH to oxaloacetate, forming malate. StepH An antiporter (blue oval) in the inner mitochondrial membrane transports malate into the matrix in exchange for a-ketoglutarate. StepH Mitochondrial malate dehydrogenase converts malate back to oxaloacetate, reducing NAD in the matrix to NADH in the process. StepH Oxaloacetate, which cannot directly cross the inner membrane, is converted to... 

The interplay of H, K, Na", and the transmembrane potential and their effect on membrane transport is a complex phenomenon. Which factors are the independent variables in a transport process and which are the dependent variables is difficult to determine. However, it is well-established that transport of many amino acids, sugars, and other carbon and nitrogen sources requires the co-transport (symport) of an ion along with it and probably the reverse transport (antiport) of a similarly charged ion. 

Two genes, rebU and rebT, could participate in rebeccamycin resistance and/or secretion. The deduced product of rebU is similar to a family of Na /H+ exchange membrane proteins which function as antiporters of Na" " or K" " and H+ and play a key role in maintaining cellular pH and other processes. RebU was found to be most similar to a putative integral membrane ion antiporter and antibiotic transporter. The second candidate for rebeccamycin resistance and/or secretion, the rebT gene... 

Antiport A membrane transport process that couples the transport of a substance in one direction across a membrane to the transport of a different substance in the other direction. Compare symport. 

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. 

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-... 

Recently, Prasad et al. cloned a mammalian Na+-dependent multivitamin transporter (SMVT) from rat placenta [305], This transporter is very highly expressed in intestine and transports pantothenate, biotin, and lipoate [305, 306]. Additionally, it has been suggested that there are other specific transport systems for more water-soluble vitamins. Takanaga et al. [307] demonstrated that nicotinic acid is absorbed by two independent active transport mechanisms from small intestine one is a proton cotransporter and the other an anion antiporter. These nicotinic acid related transporters are capable of taking up monocarboxylic acid-like drugs such as valproic acid, salicylic acid, and penicillins [5], Also, more water-soluble transporters were discovered as Huang and Swann [308] reported the possible occurrence of high-affinity riboflavin transporter(s) on the microvillous membrane. 

Takanaga, H., et al. Nicotinic acid transport mediated by pH-dependent anion antiporter and proton cotransporter in rabbit intestinal brush-border membrane. J. Pharm. Pharmacol. 1996, 48, 1073-1077. 

The recovery of neurotransmitters from synaptic clefts and their storage in cytoplasmic vesicles is accomplished by the tandem actions of the secondary transporters in plasma and vesicular membranes 84 Packaging neurotransmitters into presynaptic vesicles is mediated by proton-coupled antiporters 86... 

Figure 1. Solute transfer across an idealised eukaryote epithelium. The solute must move from the bulk solution (e.g. the external environment, or a body fluid) into an unstirred layer comprising water/mucus secretions, prior to binding to membrane-spanning carrier proteins (and the glycocalyx) which enable solute import. Solutes may then move across the cell by diffusion, or via specific cytosolic carriers, prior to export from the cell. Thus the overall process involves 1. Adsorption 2. Import 3. Solute transfer 4. Export. Some electrolytes may move between the cells (paracellular) by diffusion. The driving force for transport is often an energy-requiring pump (primary transport) located on the basolateral or serosal membrane (blood side), such as an ATPase. Outward electrochemical gradients for other solutes (X+) may drive import of the required solute (M+, metal ion) at the mucosal membrane by an antiporter (AP). Alternatively, the movement of X+ down its electrochemical gradient could enable M+ transport in the same direction across the membrane on a symporter (SP). A, diffusive anion such as chloride. Kl-6 refers to the equilibrium constants for each step in the metal transfer process, Kn indicates that there may be more than one intracellular compartment involved in storage. See the text for details...

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