Hexoses absorption

Hexose Absorption.—The relative speed of sugar absorption from the intestine is in the order galactose > glucose > fructose the concentration of sugar affects the duration but not the rate of absorption, showing that it is not a simple diffusion process. 

Give 1.0 ml of the monosaccharide-containing solution (10-70 pg of saccharide) into a centrifuge tube and mix with 20 pi of Soln. A. Add 2.5 ml of cone, sulfuric acid onto the surface of the liquid (caution, corrosive ), then cool for 10 min and keep at 25-30 °C for 10-20 min. After an additional 30 min at RT, read the absorption (hexoses) at 490 nm, pentoses at 480 nm. 

Because, on treatment with the anthrone reagents,224,225 hexoses and 5-(hydroxymethyl)-2-furaldehyde give solutions having identical spectral characteristics, dehydration is indicated to be the important reaction in this analysis. This conclusion is further supported by the reported isolation228 of 10-furfurylidene-9,10-dihydro-9-oxoanthra-cene (121) after reaction of 2-furaldehyde with anthrone, and by the fact that 121 has an absorption maximum of 600 nm, a value close to that used for pentose estimations. In similar studies,227 9,10-dihydro-10-(5-methylfurfurylidene)-9-oxoanthracene (122) was reported to have been isolated after the reaction of either L-rhamnose or 5-methyl-... 

Absorption spectra of the phenol-sulfuric acid solutions tested for total sugars show that 5-hydroxymethylfurfural from hexoses is more common in the uppermost Silurian and Devonian samples than in the earlier deposits. Furfurals from pentose sugars evidently form the bulk of the residual carbohydrates in these samples, however. There is no definite evidence as to the marine or terrestrial origin of the hexose products in the samples. 

The type 2 absorption showed only a very small deviation, regardless of whether a simple hexose or a long-chain polysaccharide was being examined. The conclusion from this observation was that the motion was an anomeric C—H deformation mode rather than a motion involving the external oxygen attached to the anomeric carbon atom. ... 

A 30 cm Protein Pak 300 SW column (Waters product no. 80013) and isocratic Waters HPLC were used to perform the chromatography studies. Solvent flow rate was fixed at 1.0 ml/min and 10 ml samples of 1-10 mg/ml were injected. Eluted components were detected by uv absorption at 280 nm. The retention times of myoglobin (18,800 MW), a-chymotrypsin (25,000 MW), hexose kinase (100,000 MW), and glucose oxidase (186,000 MW) were determined in order to calibrate the column. 

For the absorption of carbohydrates, amino acids, and peptides, a variety of transport systems following facilitated diffusion and active mechanisms have been identified on a molecular and functional level. D-Glucose is mainly absorbed via the Na -dependent transporter SGLTl in the brush-border membrane of enterocytes [18-20]. It is transported across the basolateral membrane by facilitated diffusion via the hexose transporter GLUT-2. Besides SGLTl, the Na +-independent transport protein GLUT-5 is localized in the apical enterocyte membrane, recognizing fructose as a substrate [21]. 

Wilson and Hogness showed that extensively purified UDP-D-glucose 4-epimerase from Escherichia coli contains 1 mole of tightly bound NAD per mole of enzyme, and, as an absorption peak almost identical in shape to that of NADH could be observed on addition of the substrate to the enzyme, this evidence is in accord with an oxidation-reduction mechanism involving C-4 of the hexosyl group of the UDP-hexoses. 

Several attempts have been made to facilitate the intestinal absorption and tissue distribution of less permeable componnds by ntilizing monosaccharide transport systems, throngh modification of the parent componnds to sngar analogs. The intestinal brnsh border membrane transport of hexose can be attributed to a Na" /glucose cotransporter (SGLTl) for D-glucose,... 

The Pr(II) and Nd(III) complexes of three pentoses, three hexoses and two disaccharides were characterized by various spectral and analytical techniques including FT IR, C NMR, solution absorption and solid-state diffused reflectance spectroscopy, magnetic susceptibility and CD measurements, as well as cyclic voltammetry and thermal analysis. ... 

The phenol-sulfuric acid method involves treatment of the solution containing the carbohydrate analyte (5—40pgml ) with an aqueous solution of phenol (5%, m/v) and then concentrated sulfuric acid a characteristic yellow color is produced, with an absorption maximum at 490 nm for hexoses, 480 mn for pentoses, deoxy sugars, and uronic acids. Only amino sugars do not react. Oligo- and polysaccharides are hydrolyzed to their constituent monosaccharides by the addition of concentrated... 

The second, so-called indicator reaction, provides the specificity of the method, since hexokinase also converts other hexoses, such as D-fructose and D-mannose, into their phosphorylated compounds. The formation of the coenzyme NADPH (the reduced form of nicotinamide adenine dinucleotide phosphate) can be measured photometrically, preferably at the absorption band maximum at 340 nm (see Figure 2). The hexokinase method has been internationally recommended as a reference method. 

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