Sugar and amino acid transport

GG Munck. (1972). Effects of sugar and amino-acid transport on transepithelial fluxes of sodium and chloride of short circuited rat jejunum. J Physiol 223 699-717. 

Isselbac, K.J., Deykin, D., Kaminska, E., et al. (1972) Sugar and amino-acid transport by cells in culture - Differences between normal and malignant cells. New England Journal of Medicine, 286(17), 929-933. 

Hopfer. U. (1976) Sugar and amino acid transport in animal cells. 

Mutants of E. coli lacking the amine-containing lipids PE (psdA null) or PS and PE (pssA null) are viable when grown in the presence of millimolar concentrations of Ca ", Mg, and Sr but have a complex mixture of defects in cell division, growth rate, outer membrane barrier function, energy metabolism, assembly of membrane proteins, and sugar and amino acid transport [1]. 

Owing to observations on certain competitive and reciprocal antiport relations between sugar and amino acid transport, Alvarado and Crane and Alvarado have recently postulated a new polyfunctional, mobile carrier system. involved in the uphill transport of sugars, neutral amino acids and basic amino acids in the small intestine that consists of a mosaic of fixed, specific membrane sites which acquire mobility as a result of deformations of the mobile membrane resulting in local, transient engagements of the two protein surfaces, thus allowing bound substrates to be alternately exposed to the extra- and intercellular fluids. ... 

Suspended solids also supply yeasts with nutritional elements and adsorb certain metabolic inhibitors. In fact, these two effects are related and significant The lipid fraction of suspended solids provides the principal nutritional supply (Section 13.5.1)—in particular, long chain unsaturated fatty acids (Cig) that the yeast can incorporate into its own membrane phospholipids. Sugar and amino acid transport systems across the yeast membrane are conseqnently improved. Due to their hydrophobic Upid content suspended solids are capable of adsorbing toxic inhibitive fatty acids freed in the jnice during alcoholic fermentation (Cg, Cio, C12). The combination of these two effects (lipidic nutrition and toxic fatty acid adsorption) produces a survival factor effect for yeasts (Section 3.5.2) (Ollivier et al., 1987 Alexandre et al., 1994). 

Parrish, J. E., and Kipnis, D. M., 1964, Effects of Na on sugar and amino acid transport in striated muscle, J. Clin. Invest. 43 1994. 

Facilitated diffusion and active transport share many features. Both appear to involve carrier proteins, and both show specificity for ions, sugars, and amino acids. 

This potential, or protonmotive force as it is also called, in turn drives a number of energy-requiring functions which include the synthesis of ATP, the coupling of oxidative processes to phosphorylation, a metabohc sequence called oxidative phosphorylation and the transport and concentration in the cell of metabolites such as sugars and amino acids. This, in a few simple words, is the basis of the chemiosmotic theory linking metabolism to energy-requiring processes. 

Depending upon the mechanism that is employed by the organism to accumulate the solute, internalisation fluxes can vary both in direction and order of magnitude. The kinetics of passive transport will be examined in Section 6.1.1. Trace element internalisation via ion channels or carrier-mediated transport, subsequent to the specific binding of a solute to a transport site, will be addressed in Section 6.1.2. Finally, since several substances (e.g. Na+, Ca2+, Zn2+, some sugars and amino acids) can be concentrated in the cell against their electrochemical gradient (active transport systems), the kinetic implications of an active transport mechanism will be examined in Section 6.1.3. Further explanations of the mechanisms themselves can be obtained in Chapters 6 and 7 of this volume [24,245]. 

This results in the extrusion of three positive charges for every two that enter the cell, resulting in a transmembrane potential of 50-70 mV, and has enormous physiological significance. More than one-third of the ATP utilized by resting mammalian cells is used to maintain the intracellular Na+-K+ gradient (in nerve cells this can rise up to 70%), which controls cell volume, allows neurons and muscle cells to be electrically excitable, and also drives the active transport of sugars and amino acids (see later). 

Lipid-soluble substances traverse the membrane by dissolving in the lipoid phase, and the lipid-insoluble substances penetrate only when they are small enough to pass through the pores. The absorption of large lipid-insoluble substances such as sugars and amino acids is accomplished by specialized transport processes. 

Glucose (or other sugars and amino acids) are transported across the apical... 

I. General Reviews on Na+-Coupled Solute Transport Sugars and Amino Acids Barker Ellory (1990). Experimental Physiol. 75, 3-26. 

Facilitated diffusion involves carrier-mediated transport down a concentration gradient. The existence of the carrier molecules means that diffusion down the concentration gradient is much greater than would be expected on the basis of the physicochemical properties of the drag. A much larger number of substances are believed to be transported by facilitated diffusion than active transport, including vitamins such as thiamine, nicotinic acid, riboflavin and vitamin B6, various sugars and amino acids. 

Most transporters are proteins. Small proteins can bind some substance on one side of a membrane, diffuse across the membrane, and then release that substance on the other side. Such mobile carriers may bind a single substance, or they may bind two different substances, like the proton-solute symporter portrayed in Figure 3-l4a. Candidates for transport by a proton symporter in plants include inorganic ions such as Cl- and metabolites such as sugars and amino acids. Many substances apparently move in pores or channels, which can be membrane-spanning proteins. Some channels can have a series of binding sites, where the molecule or molecules transported go from site to site through the membrane (Fig. 3-l4b). As another... 

Smith BD. Facilitated transport of sugars and amino acids through plasticized cellulose triacetate membranes. Polym Mater Sci Eng 1997 77 269-270. 

The absorption of sugars and amino acids appears to follow the same basic mechanisms as previously described for the proximal tubule of the kidney (73-77). An additional D-fructose-facilitated carrier mechanism has been located in the brush border membrane that is stereoselective and specific (78). It is Na+-independent and does not accept D- or L-glucose. After transport into the cell, the intracellular fructose concentration is decreased... 

Facilitated diffusion is a simple mechanism proposed to explain transport of water soluble compounds. The main characteristics of this transport system are that membrane permeability exceeds that predicted from partition coefficients, transport occurs down a concentration gradient, transport is saturable, and competition occurs between isomers. Facilitated diffusion has been used to explain cellular uptake of sugars and amino acids. 

Many transmembrane transporter proteins, termed secondary transporters, use the discharge of an ionic gradient to power the uphill translocation of a solute molecule across membranes. Couphng solute movement to ion transport enables these secondary transporters to concentrate solutes by a factor of 10 with a solute flux 10 faster than by simple diffusion. We have already encountered the co-transport of leucine and Na+ by LeuT, but there are many other examples. Sugars and amino acids can be transported into cells by Na+-dependent symports. Dietary glucose is concentrated in the epithelial cells of the small intestine by a Na -dependent symport, and is then... 

Absorption of vitamin C from the small intestine is a carrier-mediated process that requires sodium at the luminal surface. Transport is most rapid in the ileum and resembles the sodium-dependent transport of sugars and amino acids, but the carrier is distinct for each class of compound. Some ascorbate may also enter by simple diffusion. With dietary intake less than 100 mg/d, efficiency of absorption is 80-90%. With intake equal to the RDA, plasma ascorbate is 0.7-1.2 mg/dL, and the ascorbate pool size is 1500 mg. Scurvy becomes evident when the pool is less than 300 mg, at which point plasma ascorbate is 0.13-0.24 mg/dL. Highest tissue concentrations of ascorbate are in the adrenal gland (cortex > medulla). 

The early postprandial state is illustrated in Figure 16.4. As described, sugars and amino acids are absorbed and transported by the portal blood to the liver. The portal blood also contains a high level of lactate that is a product of enterocyte metabolism. Most lipid molecules are transported from the small intestine in lymph as... 

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