Agriculture Reference
In-Depth Information
(Hirsch et al. 1996; Wright et al. 2004), circadian cycle and luminal carbohydrates
have been observed to trigger the delivery of intracellular vesicles containing GLTs
into the apical membrane. Some selectivity of these regulatory mechanisms can be
observed since GLT5 expression at the cellular membranes depends largely on the
availability of its respective mRNA, while expression of SGLT1 and GLT2 trans-
porters depends primarily on their fast transport from intracellular storage into the
plasma membrane.
conclusIons And study toPIcs
Carbohydrates are the main source of human dietary energy intake.
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Most carbohydrates are botanical products for energy storage and transport.
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The monosaccharides glucose, galactose, and fructose are the basic build-
ing blocks of most polysaccharides, but their multimeric association gives
rise to an almost infinite number of molecular structures with one, two, or
up to millions of monosaccharide residues.
Starch is the polysaccharide with the highest consumption by the human
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population.
Salivary amylase, pancreatic amylase, SI, MGAM, and trehalase are the
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hydrolytic enzymes of the human gastrointestinal tract involved in hydroly-
sis of α-glucosidic bonds of polysaccharides for releasing their conforming
monomers. In contrast, lactase-phlorizinase is the only β-glucosidase of the
human gastrointestinal tract involved in the hydrolysis of lactose.
Given the multiplicity of chemical structures of polysaccharides, particu-
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larly starch, their physiologic effect in terms of rate and total amount of
monosaccharide release is variable for each preparation obtained from spe-
cific botanical sources.
The absorption of monosaccharides for their subsequent metabolism
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requires membrane proteins called glucose or hexose transporters that pas-
sively or actively contribute to the mobilization of monosaccharides across
the plasmatic membrane of cells.
Depending on the individual energetic expenditure, glucose, galactose,
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and fructose may follow a metabolic pathway leading to the production of
energy or storage of energy in the form of glycogen and fat.
RefeRences
Anderson, J.W. (1985) Physiological and metabolic effects of dietary fiber.
Fed. Proc.
44(14):2902-2906.
Azad, M.A. and Lebenthal, E. (1990) Role of rat intestinal glucoamylase in glucose polymer
hydrolysis and absorption.
Pediatr. Res.
28(2):166-170.
Ben Ali, H., et al. (1994) Relationship between semen characteristics, alpha-glucosidase
and the capacity of spermatozoa to bind to the human zona pellucida.
Int. J. Androl.
17(3):121-126.
Blakemore, S.J., et al. (1995) The GLUT5 hexose transporter is also localized to the basolat-
eral membrane of the human jejunum.
Biochem. J.
309(Pt 1):7-12.
