Transport of monosaccharides

Transport of monosaccharides (e.g., glucose, galactose, and fructose) into enterocytes. 

Mizuma, T. Nagamine, Y. Dobashi, A. Awazu, S. Factors that cause the P-anomeric preference of Na /glucose cotransporter for intestinal transport of monosaccharide conjugates. Biochim. Biophys. Acta 1998, 1381, 340-346. 

Elsenhans, B., Sufke, V., Blume, R., and Caspary, W. F., 1980, The influence of carbohydrate gelling agents on rat intestinal transport of monosaccharides and neutral amino acids in vitro. Clin. Sci. 59 373. 

Kleinzeller, A., Kolinska, J., and Benes, I., 1967b, Transport of monosaccharides in kidney-cortex cells, Biochem. J. 104 852. 

Kolber, A. R., and LeFevre, P. G., 1967, Evidence for carrier-mediated transport of monosaccharides in the Ehrlich ascites tumor cell, /. Gen. Physiol. 50 1907. 

LeFevre, P. G., 1954, The evidence for active transport of monosaccharides across the red cell membrane, Symp. Soc. Exp. Biol 8 118. 

Glucose and galactose enter the absorptive cells by way of secondary active transport. Cotransport carrier molecules associated with the disaccharidases in the brush border transport the monosaccharide and a Na+ ion from the lumen of the small intestine into the absorptive cell. This process is referred to as "secondary" because the cotransport carriers operate passively and do not require energy. However, they do require a concentration gradient for the transport of Na+ ions into the cell. This gradient is established by the active transport of Na+ ions out of the absorptive cell at the basolateral surface. Fructose enters the absorptive cells by way of facilitated diffusion. All monosaccharide molecules exit the absorptive cells by way of facilitated diffusion and enter the blood capillaries. 

Mizuma, T., K. Ohta, and S. Awazu. The beta-anomeric and glucose preferences of glucose transport carrier for intestinal active absorption of monosaccharide conjugates. Biochim. Biophys. Acta 1994, 1200, 117-122. 

B. Uptake of monosaccharides and disaccharides by intestinal mucosal cells is mediated by a variety of transporters. 

The demonstration by Crane (1960, 1965) that Na+ ions were essential for the translocation of monosaccharides by segments of the intestine brought in a new era of understanding of the central role of ion coupled transport, particularly in higher organisms. While Na+ is clearly the predominant cation involved in cation driven solute accumulation in mammalian systems, current work has provided examples of H+ driven solute transport in intestine and kidney (Jessen et al., 1989 Ganapathy and Leibach, 1986). Conversely, in yeast and bacteria, H+ driven mechanisms are in the majority (Seaston et al., 1973 Hirata et al., 1973), but examples of Na+-cou-pled fluxes exist, e.g., proline transport (Dibrov, 1991). 

The mechanism by which amino acids are absorbed is conceptually identical to that of monosaccharides. The lumen plasma membrane of the absorptive ceU bears a number of different Na+ amino acid symporters. Again it is the Na gradient across the ceU that drives this process. Na+-independent transporters on the basolateral membrane export amino acids to the extracellular space. The resulting osmotic gradient contributes to water absorption. 

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