Fructose tolerance

For values during an intravenous fructose tolerance test in controls and individuals with deficiencies of fructokinase, fructaldolase, and fructose- 1,6-bisphosphatase, see Steinmann et al. [36]. 

Hereditary fructose intolerance affects one in 21 000 persons, and there have been more than 12 severe complications caused by these solutions, several lethal. Since a prior history of fructose intolerance is often not obtained, it has been argued that the use of fructose- and sorbitol-containing infusion fluids must be regarded as offering doubtful advantage but carrying definite lethal risk, and that their use should be discontinued. A modified intravenous fructose tolerance test should at least be carried out before infusions of fructose or sorbitol are giveu (8). 

Chambers and Pratt (Cl) reported the case of a 24-year-old female who had vomiting and dyspepsia following fructose or cane sugar ingestion. Her fructose tolerance curve was not abnormal, and insufiBcient studies were done to permit diagnosis. 

In contrast to hereditary fructose intolerance where lack of fructose-1-phosphate aldolase (Levin et al. 1963) in serum and liver is a prominent feature, liver fructose-1-phosphate aldolase activity in TSD is only reduced to approximately 60%, and fructose tolerance is not impaired in the latter disorder (Schneck et al. 1965), while in the former accumulation of fructose-1-phosphate and hypoglycemia... 

G. Perle, and B. W. Volk Fructose tolerance in Tay-Sachs disease. Pediatrics 36, 272 (1965a). 

A galactose or fructose tolerance test normally results in a rise in blood sugar levels as a result of their conversion in the liver by a series of enzymes including glucose-6-phosphatase. In Type I glycogen storage disease this does not occur. 

Sucrose, in contrast, is a disaccharide of almost universal appeal and tolerance. Produced by many higher plants and commonly known as table sugar, it is one of the products of photosynthesis and is composed of fructose and glucose. Sucrose has a specific optical rotation, of +66.5°, but an... 

In a previous work, using D-fructose pyran- and furan- forms as inhibitors of D-fructose transport in CHO (Chinese Hamsters Ovary)-GLUT5 cells, Rollin, Holman and co-workers established that both ring forms were tolerated. The approach used was to block each hydroxyl function with allylic ether it was concluded that two sites, 0-2 (pyranose and furanose) and 0-6 (furanose) could be modified and addressed a visualization of vital interactions with the protein. These interactions were considered to occur because the D-fructofuranose form is relatively symmetrical for that reason, the binding site can arise either in anomeric center side or on the other side of the molecule. Hence D-fructopyranose appears to present to GLUT5 transporter by hydroxyl 3, 4, 5 recognition (Fig. 3). 

Limiting Supersaturation for Nucleation. Like sucrose, D-fructose solutions can tolerate a high degree of supersaturation without nucleating, even in the presence of seed crystals. This is the metastable region on the Miers supersolubility diagram (9). 

D-fructose 1,6-bisphosphate 2 (FruA E.C. 4.1.2.13), D-tagatose 1,6-bisphosphate 4 (TagA E.C. 4.1.2.40), L-fuculose 1-phosphate 5 (FucA, E.C. 4.1.2.17), and L-rhamnulose 1-phosphate 4 (RhuA, E.C. 4.1.2.19). From previous studies, we have DHAP aldolases with all four possible specificities readily available, we have demonstrated their broad substrate tolerance for variously substituted aldehydes, and we have investigated their stereoselectivity profile with non-natural substrates [3-6]. 

Table 4. Substrate tolerance of fructose 1,6-bisphosphate aldolase...

Fructose 1,6-biphosphate aldolase from rabbit muscle in nature reversibly catalyzes the addition of dihydroxyacetone phosphate (DHAP) to D-glyceraldehyde 3-phosphate. The tolerance of this DHAP-dependent enzyme towards various aldehyde acceptors made it a versatile tool in the synthesis of monosaccharides and sugar analogs [188], but also of alkaloids [189] and other natural products. For example, the enzyme-mediated aldol reaction of DHAP and an aldehyde is a key step in the total synthesis of the microbial elicitor (—)-syringolide 2 (Fig. 35a) [190]. 

Sorbitol is widely used in a number of pharmaceutical products and occurs naturally in many edible fruits and berries. It is absorbed more slowly from the gastrointestinal tract than sucrose and is metabolized in the liver to fructose and glucose. Its caloric value is approximately 16.7J/g (4cal/g). Sorbitol is better tolerated by diabetics than sucrose and is widely used in many sugar-free liquid vehicles. However, it is not considered to be unconditionally safe for diabetics. 

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