scholarly journals Galactose transport across the hamster small intestine; the effect of sodium electrochemical potential gradients

1971 ◽  
Vol 212 (1) ◽  
pp. 277-286 ◽  
Author(s):  
Anthony P. Smulders ◽  
Ernest M. Wright
Keyword(s):  
Small Intestine ◽  
Electrochemical Potential ◽  
Galactose Transport ◽  
Potential Gradients

scholarly journals Function Trumps Form in Two Sugar Symporters, LacY and vSGLT

2021 ◽  
Vol 22 (7) ◽  
pp. 3572
Author(s):  
Jeff Abramson ◽  
Ernest M. Wright
Keyword(s):  
Binding Site ◽  
Sugar Transport ◽  
Electrochemical Potential ◽  
Inverted Repeats ◽  
Side Chains ◽  
Transmembrane Helices ◽  
Central Cavity ◽  
Potential Gradients ◽  
Sodium Binding ◽  
Major Facilitator

Active transport of sugars into bacteria occurs through symporters driven by ion gradients. LacY is the most well-studied proton sugar symporter, whereas vSGLT is the most characterized sodium sugar symporter. These are members of the major facilitator (MFS) and the amino acid-Polyamine organocation (APS) transporter superfamilies. While there is no structural homology between these transporters, they operate by a similar mechanism. They are nano-machines driven by their respective ion electrochemical potential gradients across the membrane. LacY has 12 transmembrane helices (TMs) organized in two 6-TM bundles, each containing two 3-helix TM repeats. vSGLT has a core structure of 10 TM helices organized in two inverted repeats (TM 1–5 and TM 6–10). In each case, a single sugar is bound in a central cavity and sugar selectivity is determined by hydrogen- and hydrophobic- bonding with side chains in the binding site. In vSGLT, the sodium-binding site is formed through coordination with carbonyl- and hydroxyl-oxygens from neighboring side chains, whereas in LacY the proton (H3O+) site is thought to be a single glutamate residue (Glu325). The remaining challenge for both transporters is to determine how ion electrochemical potential gradients drive uphill sugar transport.

Inhibition of D-Galactose Transport Across the Small Intestine of Rabbit by Zinc

1992 ◽  
Vol 39 (1-10) ◽  
pp. 687-695 ◽  
Author(s):  
María-Carmen Rodriguez Yoldi ◽  
J.E. Mesonero ◽  
M.-J. Rodriguez Yoldi
Keyword(s):  
Small Intestine ◽  
Galactose Transport

Membranes for artificial photosynthesis

2017 ◽  
Vol 10 (6) ◽  
pp. 1320-1338 ◽  
Author(s):  
Sakineh Chabi ◽  
Kimberly M. Papadantonakis ◽  
Nathan S. Lewis ◽  
Michael S. Freund
Keyword(s):  
Charge Transport ◽  
Artificial Photosynthesis ◽  
Electrochemical Potential ◽  
Potential Gradients

Membrane-based architectures enable optimization of charge transport and electrochemical potential gradients in artificial photosynthesis.

Potassium transport by turtle colon: active secretion and active absorption

1984 ◽  
Vol 246 (3) ◽  
pp. C315-C322 ◽  
Author(s):  
D. R. Halm ◽  
D. C. Dawson
Keyword(s):  
Simple Model ◽  
Short Circuit ◽  
Potassium Transport ◽  
Electrochemical Potential ◽  
Free Solution ◽  
Active Secretion ◽  
Basolateral Membranes ◽  
Potential Gradients ◽  
Absorptive Flux ◽  
K Transport

Measurement of transepithelial potassium fluxes in the absence of transmural electrochemical potential gradients showed that the isolated turtle colon can actively absorb and actively secrete K+. Under short-circuit conditions the active secretory flow was inhibited by mucosal amiloride, whereas the absorptive flow was unaffected by the diuretic. The effects of ouabain and barium on secretory flow were consistent with a simple model involving basolateral uptake by an Na+-K+-ATPase and conductive exist across the apical and basolateral membranes. The active absorptive flux was blocked by mucosal ouabain and by serosal barium. The opposing active flows clearly represented cellular K+ transport, whereas paracellular K+ flows behaved as expected for a free-solution shunt.

Intestinal sugar transport: does the Na+ gradient provide all the energy?

1986 ◽  
Vol 250 (4) ◽  
pp. G448-G454
Author(s):  
R. D. Baker
Keyword(s):  
Small Intestine ◽  
Concentration Ratio ◽  
Apical Membrane ◽  
Sugar Transport ◽  
Tissue Uptake ◽  
Coupling Ratio ◽  
Intracellular Na Activity ◽  
Galactose Transport ◽  
Net Fluxes

It has not yet been established that the energy released from the Na+ gradient during Na+-sugar cotransport by small intestine is sufficient, by itself, to drive uphill sugar transport under conditions in which other sources of energy are available and in which sugar is being vigorously transported. This work attempts to test the thermodynamic sufficiency of the Na+ mechanism under such conditions using hamster jejunum in vitro. From data on tissue uptake of D-galactose and unstirred layer considerations, the concentration ratio for galactose across the apical membrane during mucosal-to-serosal galactose transport was estimated to be at least 50 when concentration in the bulk mucosal solution was 2.2 mM. This estimate and reasonable assumptions regarding intracellular Na+ activity and apical membrane potential were used to calculate the minimum physiological coupling ratio (i.e., the ratio of coupled net fluxes of Na+ and galactose) required if all the energy necessary for galactose transport is transferred from Na+. The minimum physiological coupling ratio required was roughly 1.4. An estimate based on the ratio of transepithelial chord permeabilities to galactose, instead of the apical concentration ratio, would be higher. The measured physiological coupling ratio (0.4) was considerably less than that required. For reasons discussed, this result should be interpreted with caution. It can be concluded that the issue of energetic adequacy is not yet settled.

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