Trioses-Hexoses

1 Trioses - Hexoses. - Full details have been published on a high yielding bulk synthesis of O-isopropylidene-D-glyceraldehyde from D-mannitol.  

Reevg rtfe TMSCN.ZrLig ii, Raney Ni, HCOaH.EtOH 

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Meyerhof and Schulz86 studied this reaction in trisodium phosphate solution, and regarded it as coming to a triose-hexose equilibrium containing 92 % of hexose. Berl and Feazel67 examined the kinetics of hexose formation from trioses in alkaline solution, and noted that 75-90% of hexulose is formed from DL-glycerose alone, but that the yield is lower (about 60%) when dihydroxyacetone is added in equivalent quantity. Paper chromatog-... 

Aldolizations of trioses, with formation of hexoses, have been observed in several investigations. Meyerhof estimated that the triose-hexose equilibrium mixture from the condensation of OL-glycerose with 1,3-dihydroxy-2-propanone (in trisodium phosphate solution) contained 92% of hexose. Berl and Feazel, in their kinetic examination of this aldolization in sodium hydroxide solution, were unable to detect any triose by paper chromatography at the end of the reactions. Pyruvaldehyde formation complicates any glycerose or 1,3-dihydroxy-2-propanone reaction in alkaline medium, and this fact probably accounts for some of the disappearance of triose from these mixtures. Nevertheless, aldolizations of these short-chain sugars are side reactions to be reckoned with, whenever circumstances permit their occurrence. 

The pentoses are not fermented by yeast enzymes, whereas most hexoses are readily attacked. Alcoholic fermentation has been observ ed among trioses, hexoses, and nonoses, which is in agreement with the equation ... 

The hexose phosphate, fructose-1,6-diphosphate, is split by aldolase into two triose phosphates glyceraldehyde-3-phosphate and dihydroxyacetone phosphate. Aldolase consists of four 40-kDa subunits. Three tissue-specific forms exist in human tissues aldolase A (ubiquitous and very active in the muscle), aldolase B (liver, kidney, and small intestine), and aldolase C (specific to the brain). These three isozymes have nearly the same molecular size but differ in substrate specificity,... 

Triose phosphate isomerase (TPI) catalyzes the interconversion of glyceralde-hyde-3-phosphate and dihydoxyacetone phosphate and has an important role in glycolysis, gluconeogenesis, fatty acid synthesis, and the hexose monophosphate pathway. Red blood cell TPI activity measured in vitro is approximately 1000 times that of Hx, the least active glycolytic enzyme. TPI is a dimer of identical subunits, each of molecular weight 27,000, and does not utilize cofactors or metal ions. Posttranslational modification of one or both subunits may occur by deamidination, resulting in multiple forms of the enzymes and creating a complex multibanded pattern on electrophoresis. 

D-fructose, and of their optical isomers, a truly remarkable achievement (see Fig. 1). Thus, encouragement was given to the formaldehyde theory. Paper chromatography shows formose to be a complex mixture containing glycolaldehyde, trioses, tetroses, pentoses, and hexoses.62- 63 Schmitz64 re-... 

D-afe-o-Heptulose (sedoheptulose) (XXXVII) has been synthesized from D-erythrose (XXXVIII) plus triose phosphate, using an aldolase preparation from peas.169 Aldolases from yeast and from rat liver also form heptu-lose phosphate from these substrates.7S(o) 170(a) Crystalline muscle aldolase causes the formation of L-jrZwco-heptulose (XXXVIIa) from a mixture of L-erythrose (XXXVTIIa) and hexose diphosphate.170(b)... 

D-lAreo-Pentulose 5-phosphate + D-erythrose 4-phosphate tran>lcetolaM, D-fructose 6-phosphate + D-glycerose 3-phosphate 2 Triose phosphate —> hexose phosphate + inorganic phosphate... 

Figure 4.17 The trioses D-glyceraldehyde (aldose) and dihydroxyacetone (ketose), the pentose D-ribose, the hexoses D-galactose and D-glucose (aldoses) and the ketohexose D-fructose in their open chain forms. The configuration of the asymmetrical hydroxyl group on the carbon, the furthest away from the aldehyde or ketone group, determines the assignment of D- or L-configuration.

Figure 14. Principle for measuring bidirectional fluxes by 13C metabolic flux analysis. In a carbon labeling experiment, 1 13C glucose is provided in the medium, and the culture is grown until a steady state is reached. Glucose can either go directly via the hexose phosphate pool (Glu 6P and Fru 6P) into starch, resulting in labeling hexose units of starch only at the Cj position, or it can be cleaved to triose phosphates (DHAP and GAP), from which hexose phosphates can be resynthesized, which will result in 50% labeling at both the Ci and the C6 position (assuming equilibration of label by scrambling at the level of triose phosphates). From the label in the hexose units of starch, the steady state fluxes at the hexose phosphate branchpoint can be calculated for example, if we observe 75% label at the Ci and 25% at the C6 position, the ratio of vs to V7 must have been 1 to 1. All other fluxes can be derived if two of the fluxes of Vi, V6, and V7 are known (e.g., V2 vi V3 V5 + v6).

A. R. Fernie, A. Roscher, R. G. Ratcliffe, and N. J. Kruger, Fructose 2,6 bisphosphate activates pyrophosphate fructose 6 phosphate 1 phosphotransferase and increases triose phosphate to hexose phosphate cycling in heterotrophic cells. Planta 212, 250 263 (2001). 

The natural substrate for the dehydrogenase, glyceraldehyde-3-phosphate (G-3-P), had been synthesized earlier by Hermann Fischer, Emil Fischer s son, and Baer in 1932. In 1934 Meyerhof and Lohmann synthesized hexose diphosphate, establishing it to be fructose 1,6 bisphosphate (F-l, 6 bis P). With F-1,6 bisP as substrate and hydrazine to trap the aldehydic and ketonic products of the reaction, G-3-P was identified in the mixture of G-3-P and dihydroxyacetone phosphate which resulted. Triose phosphate isomerase was then isolated and the importance of phosphorylated 3C derivatives established. 

In the well known "transketolase reaction" [9] for instance, the transfer of the fragment H0CH2-C=0 from a hexose to a triose takes place via the "active glycoaldehyde" (Scheme 5.8) ... 

Glyceraldehyde (2,3-dihydroxypropanal), acetol, and dihydroxyace-tone form 1-5% of biacetyl and a number of other products, including pyrocatechol and 33, after exposure to aqueous alkali at 300°. Such trioses as glyceraldehyde and dihydroxyacetone have been shown to form various hexoses by aldol reaction. Aldolization, followed by retro-aldoliza-tion, is undoubtedly a major consideration when three-, four-, and five-carbon sugars are subjected to elevated temperatures. Differences in thermolysis products, partially quantitative, are noticeable at 100°, but, at temperatures near 300°, it is quite difficult, if not impossible, to determine if the starting material was a triose, a tetrose, or a pentose. 

Aus Triose-, Tetrose- und Pentose-osazonen entstehen in alkoholischer Losung 3-Alkoxy-osazone (vgl. S. 457), wahrend Hexose-osazone intra-molekular an intermediar gebildete Phenylhydrazono-en-phenyl-azo-Systeme zu 3.6-Anhydro-osazonen addieren ) (vgl. S. 458). 

Aldose sugars make up a large part of the carbohydrate family, but the ones that are really worth knowing are part of the D-family. The simplest of these D-sugars is the triose glyceraldehyde. From there you have 2 tetroses, 4 pentoses, and 8 hexoses. Each of these aldose sugars has an enantiomer. 

It remains undecided whether the formation of small amounts of glycerol reported by Oppenheimer in the case of zymase extract is due to a ph3rtochemical reduction of trioses. If hexoses are fermented in the presence of trioses with ordinary fresh yeasts which do not attack dihy-droxyacetone and glyceraldehyde, the added trioses are recovered practically unaltered after the disappearance of the hexoses. 

Trivial names are common in carbohydrate nomenclature. Fifteen of them form the basis of the systematic nomenclature. They are assigned to the simple aldoses (polyhydroxyaldehydes), from triose to hexoses. 

Carbohydrates such as trioses, tetroses, pentoses, hexoses and polysaccharides are extremely important molecules in nature. The biological significance of oligosaccharides for cell-cell interaction is increasingly understood (Fukuda and Hindsgaul, 1994). The simple carbohydrates are the building blocks of oligo- and polysaccharides. Biocatalysis... 

It should be noted that the aldehydic carbon atom of the triose enediol released from the reducing end originates from C-3 of the hexose, whereas the carbonyl group of the D-glyceraldehyde formed from the nonreducing end originates from C-4. Thus, in the absence of isomerization, hexoses labeled at either C-l or C-6 would mainly yield lactic-3-14C acid. However, extensive isomerization does occur, and lactic-2-14C acid and lactic-I-14C acid are also found in considerable proportion. The presence of lactic-2-14C acid is explained by the reaction of the dicarbonyl compound 78 that undergoes a benzilic... 

Depending on the number of carbon atoms present, monosaccharides are classihed as triose, tetrose, pentose or hexose, containing three, four, five or six carbon atoms, respectively. Glucose is a hexose as it contains six carbon atoms. Sometimes, monosaccharides are classified more precisely to denote the functional group as well as the number of carbon atoms. For example, glucose can be classified as an aldohexose, as it contains six carbon atoms as well as an aldehyde group. 

FIGURE 7-1 Representative monosaccharides, (a) Two trioses, an aldose and a ketose. The carbonyl group in each is shaded, (b) Two common hexoses. (c) The pentose components of nucleic acids. D-Ribose is a component of ribonucleic acid (RNA), and 2-deoxy-o-ribose is a component of deoxyribonucleic acid (DNA). 

FIGURE 20-11 Transketolase-catalyzed reactions of the Calvin cycle, (a) General reaction catalyzed by transketolase the transfer of a two-carbon group, carried temporarily on enzyme-bound TPP, from a ketose donor to an aldose acceptor, (b) Conversion of a hexose and a triose to a four-carbon and a five-carbon sugar (step of Fig. 20-10). (c) Conversion of seven-carbon and three-carbon sugars to two pentoses (step of Fig. 20-10). 

Although we have described metabolic transformations in plant cells in terms of individual pathways, these pathways interconnect so completely that we should instead consider pools of metabolic intermediates shared among these pathways and connected by readily reversible reactions (Fig. 20-37). One such metabolite pool includes the hexose phosphates glucose 1-phosphate, glucose 6-phosphate, and fructose 6-phosphate a second includes the 5-phosphates of the pentoses ri-bose, ribulose, and xylulose a third includes the triose phosphates dihydroxyacetone phosphate and glycer-aldehyde 3-phosphate. Metabolite fluxes through these... 

The individual pathways of carbohydrate metabolism in plants overlap extensively they share pools of common intermediates, including hexose phosphates, pentose phosphates, and triose phosphates. Transporters in the membranes of chloroplasts, mitochondria, amyloplasts, and peroxisomes mediate the movement of sugar phosphates between organelles. The direction of metabolite flow through the pools changes from day to night. 

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