Sucrose pathways

Ou-Lee, T.-M., and Setter, T. 1985b. Enzyme activities of starch and sucrose pathways and growth of apical and basal maize kernels. Plant PhysioL 79, 848-851. 

Alitame (trade name Adame) is a water-soluble, crystalline powder of high sweetness potency (2000X, 10% sucrose solution sweetness equivalence). The sweet taste is clean, and the time—intensity profile is similar to that of aspartame. Because it is a stericaHy hindered amide rather than an ester, ahtame is expected to be more stable than aspartame. At pH 2 to 4, the half-life of aUtame in solution is reported to be twice that of aspartame. The main decomposition pathways (Fig. 6) include conversion to the unsweet P-aspartic isomer (17) and hydrolysis to aspartic acid and alanine amide (96). No cyclization to diketopiperazine or hydrolysis of the alanine amide bond has been reported. AUtame-sweetened beverages, particularly colas, that have a pH below 4.0 can develop an off-flavor which can be avoided or minimized by the addition of edetic acid (EDTA) [60-00-4] (97). 

The pentose phosphate pathway is an alternative route for the metabolism of glucose. It does not generate ATP but has two major functions (1) The formation of NADPH for synthesis of fatty acids and steroids and (2) the synthesis of ribose for nucleotide and nucleic acid formation. Glucose, fructose, and galactose are the main hexoses absorbed from the gastrointestinal tract, derived principally from dietary starch, sucrose, and lactose, respectively. Fructose and galactose are converted to glucose, mainly in the liver. 

Figure 5 Model of phosphorus (P) deficiency-induced physiological changes associated with the release of P-mobilizing root exudates in cluster roots of white lupin. Solid lines indicate stimulation and dotted lines inhibition of biochemical reaction sequences or mclaholic pathways in response to P deliciency. For a detailed description see Sec. 4.1. Abbreviations SS = sucrose synthase FK = fructokinase PGM = phosphoglueomutase PEP = phosphoenol pyruvate PE PC = PEP-carboxylase MDH = malate dehydrogenase ME = malic enzyme CS = citrate synthase PDC = pyruvate decarboxylase ALDH — alcohol dehydrogenase E-4-P = erythrosc-4-phosphate DAMP = dihydraxyaceConephos-phate APase = acid phosphatase.

I. Koch, B. H. Junker, and M. Heiner. Application of Petri net theory for modeling and validation of the sucrose breakdown pathway in the potato tuber. Bioinformatics 21(7), 1219 1226 (2005). 

Cremaschi et al. [39] investigated transepithelial pathways of eel calcitonin, corticotrophin, sucrose, and polyethylene glycol-4000 (PEG-4000) transport across the nasal epithelium using rabbit nasal mucosa mounted on Ussing chamber that was maintained at 27°C. The electrical parameters of the tissues were those of leaky epithelium that allow macromolecules to permeate paracellularly their observation was similar to the finding made by McMartin et al. [40] in which the authors described the nasal epithelium as leaky with... 

Fructose is found in honey and fruit and as part of the disaccharide sucrose (common table sugar). Sucrose is hydrolyzed by intestinal brush border sucrase, and the resulting monosaccharides, glucose and fructose, are absorbed into the portal blood. The liver phosphorylates frurtose and cleaves it into glyceraldehyde and DHAP. Smaller amounts are metabolized in renal proximal tubules. The pathway is shown in Figure 1-12-7 important enzymes to remember are ... 

Several products were also detected in base-degraded D-fructose solution acetoin (3-hydroxy-2-butanone 62), l-hydroxy-2-butanone, and 4-hydroxy-2-butanone. Three benzoquinones were found in the product mixture after sucrose had been heated at 110° in 5% NaOH these were 2-methylbenzoquinone, 2,3,5-trimethylbenzoquinone, and 2,5-dimethyl-benzoquinone (2,5-dimethyl-2,5-cyclohexadiene-l,4-dione 61). Compound 62 is of considerable interest, as 62 and butanedione (biacetyl 60) are involved in the formation of 61 and 2,5-dimethyl-l,4-benzenediol (63) by a reduction-oxidation pathway. This mechanism, shown in Scheme 10, will be discussed in a following section, as it has been proposed from results obtained from cellulose. 

Catechol and related phenolics 13,16,19, 31, and 32 were also isolated after alkaline treatment of D-glucose and sucrose. Several other substituted acetophenones were isolated. The mechanism of formation of phenolic compounds from monosaccharides under alkaline conditions has yet to be thoroughly investigated. The similarity in the types of aromatic products from D-glucose and D-xylose indicates the formation of the same C2, C3, or C4 fragments, with subsequent recombination and cycliza-tion. Base-catalyzed aldol reactions are, no doubt, predominant pathways in the initial formation of these aromatic products. 

Phosphoric acid esters of the ketopentose D-ribulose (2) are intermediates in the pentose phosphate pathway (see p.l52) and in photosynthesis (see p.l28). The most widely distributed of the ketohexoses is D-fructose. In free form, it is present in fruit juices and in honey. Bound fructose is found in sucrose (B) and plant polysaccharides (e.g., inulin). 

SCHEME 22. A new pathway to the 2,3-manno-epoxide derivative of sucrose (1986). 

SCHEME 32. A.K.M.S. Kabir s pathway to 4-fluoro-galacto-sucrose with Hough and Richardson (1984). 

Fig. 25.1 The three pathways for the preparation of natural flavours. The first two involve the extraction of the flavour or precursors from natural sources. The precursors can then be converted to the natural flavour by enzymes extracted from plants or microorganisms. The last method is the de novo synthesis of the flavour by microorganisms growing on simple substrates such as glucose and sucrose...

Another line of evidence that supports this pathway comes from a consideration of stereochemistry. In 1953, D. E. Koshland Jr. pointed out the significance of the fact that the formation of glucose-1-phosphate [5] from sucrose [6] occurs with retention of configuration at C-l of the glucose moiety. He postulated that a single displacement, in enzymic chemistry as in... 

Although the reactions of gluconeogenesis are the same in all organisms, the metabolic context and the regulation of the pathway differ from one species to another and from tissue to tissue. In this section we focus on gluconeogenesis as it occurs in the mammalian liver. In Chapter 20 we show how photosynthetic organisms use this pathway to convert the primary products of photosynthesis into glucose, to be stored as sucrose or starch. 

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