Antiporters, natural

Hunte C, Screpanti E, Venturi M, Rimon A, Padan E, Michel H (2005) Structure of a Na+/H+ antiporter and insights into mechanism of action and regulation by pH. Nature 435 1197-1202. 

Because of its cyclic nature, this process presents analogies with molecular catalysis it may be considered as physical catalysis operating a change in location, a translocation, on the substrate, like chemical catalysis operates a transformation into products. The carrier is the transport catalyst which strongly increases the rate of passage of the substrate with respect to free diffusion and shows enzyme-like features (saturation kinetics, competition and inhibition phenomena, etc.). The active species is the carrier-substrate supermolecule. The transport of substrate Sj may be coupled to the flow of a second species S2 in the same (symport) or opposite antiport) direction. 

Picollo, A., Pusch, M. 2005. Chloride/proton antiporter activity of mammalian CLC proteins C1C-4 and C1C-5. Nature 436 420-423. 

Many compounds that perturb the cellular cytoskeleton affect phagocytosis and macropinocytosis. Binding to actin filaments by the natural product cytochalasin D blocks both of these uptake mechanisms. Disruption of microtubules by the antimitotic agents colchicine and nocodazole inhibits macropinocytosis and affects some mechanisms of phagocytosis. The diuretic drug amiloride, which is an inhibitor of Na+/H+ antiporters, selectively blocks macropinocytosis. By activating protein kinase C, phorbol esters represent a class of small molecules that promote macropinocytosis. 

The Inner membrane of brown-fat mitochondria contains thermogenin, a protein that functions as a natural uncoupler of oxidative phosphorylation. Like synthetic uncouplers, thermogenin dissipates the proton-motive force across the Inner mitochondrial membrane, converting energy released by NADH oxidation to heat. Thermogenin is a proton transporter, not a proton channel, and shuttles protons across the membrane at a rate that is a millionfold slower than that of typical Ion channels. Its amino acid sequence is similar to that of the mitochondrial ATP/ADP antiporter, and it functions at a rate that Is characteristic of other transporters (see Figure 7-2). 

H. Barbier-Brygoo, Nature, 442, 939-942 (2006). The Nitrate/Proton Antiporter AtCLCa Mediates Nitrate Accnmnlation in Plant Vacuoles. 

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