Chemistry
Conversion of Glucose to Fructose
The conversion of glucose to fructose involves the enzymatic process known as isomerization, where the glucose molecule is rearranged to form fructose. This reaction is catalyzed by the enzyme glucose isomerase, which facilitates the conversion of the aldehyde group in glucose to a ketone group in fructose. This process is important in the production of high-fructose corn syrup and various other industrial applications.
Written by Perlego with AI-assistance
Related key terms
1 of 5
8 Key excerpts on "Conversion of Glucose to Fructose"
eBook - PDFDietary Sugars
Chemistry, Analysis, Function and Effects
- Victor R Preedy(Author)
- 2012(Publication Date)
- Royal Society of Chemistry(Publisher)
The aim of these pathways is to convert these other monosaccharides to intermediates in the glycolytic pathway. Thereafter, the carbon atoms can continue down this pathway and, under aerobic conditions, enter the tricarboxylic acid cycle. In higher organisms, the metabolism of glucose and other sugars occurs OH HO OH OH HO O [O] [O] O OH O H 3 C H 2 C + + Other products CO 2 OH HO OH OH HO O [H] OH HO OH OH HO HO OH HO OH OH HO HO + Sorbitol (50%) Mannitol (50%) (b) (a) Figure 8.4 The oxidation and reduction of fructose. (a) Oxidation with strong oxi-dising agents (represented here as [O]) yields a complex mixture of pro-ducts. The ultimate product is carbon dioxide. (b) Reduction with, for example, sodium borohydride (represented here as [H]) results in an equimolar mixture of the sugar alcohols sorbitol and mannitol. 119 Fructose Chemistry simultaneously and often in the same cell. In many bacteria and fungi, the metabolism of monosaccharides is stringently controlled at the genetic level. Often, glucose is the preferred carbon and energy source and when this com-pound is present, the genes encoding the enzymes for the degradation of alternative sugars are strongly repressed. Only under conditions of low, or zero, glucose are these genes expressed and, therefore, elaborate control mechanisms are required to ensure that these changes in gene expression occur rapidly and under the appropriate conditions. 8.3.1 Phosphorylation of Fructose Catalysed by Fructokinase Fructokinase (ketohexokinase; EC 2.7.1.3) catalyses the phosphorylation of fructose at position 1 at the expense of the phosphate donor, ATP. This reaction is the main pathway for the utilisation of fructose in mammalian tis-sues which have high glucose concentrations and also in micro-organisms, which induce genes encoding the enzymes of fructose metabolism in response to metabolic conditions (see above).
eBook - PDF- P Karlson(Author)
- 1975(Publication Date)
- Academic Press(Publisher)
8. The Metabolism of Fructose Cane sugar (sucrose) is composed of glucose and fructose, as will be explained in Chapter XVII,2, and is decomposed to these constituents in the intestines. Thus, fructose is one of the regular components of our diet. In some circumstances, fructose can make up a considerable part of all the carbohydrates ingested. Fructose phosphates are intermediates in the breakdown of glucose according to the Embden-Meyerhof pathway, but free fructose is broken down in a different fashion. At first it is phosphorylated by a fructokinase and ATP to produce fructose 1-phosphate. 1 The phosphate is split by a specific enzyme, 1-phosphofructoaldolase, to dihydroxyacetone phosphate and glyceraldehyde. This last step corresponds to the aldolase reaction of glycolysis except that the resulting glyceraldehyde is unphos-phorylated. Free glyceraldehyde can now follow a number of different pathways. Most of it is phosphorylated to glyceraldehyde 3-phosphate and thus can enter the glycolytic pathway. Some of it is reduced to glycerol through the action of NADH-dependent alcohol dehydrogenase. Last, some glyceraldehyde can be oxidized directly (un-H 2 C -0 — fo H 2 C -O H G l y c o l y s i s F r u c t o s e 1 - (P) H -C -O H H -C -O H H 2 C -O H H -Ç -O H H 2 C -O H H 2 C -O H G l y c e r a l d e h y d e G l y c e r a t e G l y c e r o l 7 P h o s p h o r y l a t i o n in the 1-position is f a v o r e d p r o b a b l y because free fructose occurs p r e d o m i n a n t l y in its pyranose f o r m (the o x y g e n bridges between C-2 a n d C -6). T h e 6 -h y d r o x y l g r o u p is thus blocked a n d cannot be p h o s p h o r y l a t e d . 316 X V . S I M P L E S U G A R S , M O N O S A C C H A R I D E S phosphorylated) to glycerate, which then is phosphorylated at position 2. The last step is a connection to the Embden-Meyerhof degradative pathway, but without the gain of one ATP.
eBook - PDF- H. Stephen Stoker(Author)
- 2015(Publication Date)
- Cengage Learning EMEA(Publisher)
The entry of fructose into the glycolytic pathway involves phosphorylation by ATP to produce fructose 1-phosphate, which is then split into two trioses— glyceraldehyde and dihydroxyacetone phosphate. Dihydroxyacetone phosphate enters glycolysis directly; glyceraldehyde must be phosphorylated by ATP to glyceraldehyde 3-phosphate before it enters the pathway (Figure 13-5). Regulation of Glycolysis Glycolysis, like all metabolic pathways, must have control mechanisms associated with it. In glycolysis, the control points are Steps 1, 3, and 10 (see Figure 13-3). Step 1, the conversion of glucose to glucose 6-phosphate, involves the enzyme hexokinase. This particular enzyme is inhibited by glucose 6-phosphate, the substance produced by its action (feedback inhibition; Section 10-9). At Step 3, where fructose 6-phosphate is converted to fructose 1,6-bisphosphate by the enzyme phosphofructokinase, high concentrations of ATP and citrate inhibit Two pyruvates ADP Dihydroxyacetone phosphate Fructose 1,6-bisphosphate Fructose 6-phosphate Two glyceraldehyde 3-phosphates Two 1,3-bisphospho-glycerates Glyceraldehyde Glucose 6-phosphate Glucose 1-phosphate Four steps Galactose Fructose 1-phosphate Fructose ATP ADP ATP ADP 2 NAD + + 2 P i 2 NADH + 2 H + ADP Glucose ATP 4 ADP 4 ATP 2 H 2 O ATP ADP ATP Step 3 Step 4 Step 5 Step 6 Step 1 Step 2 Steps 7–10 Figure 13-5 Entry points for fructose and galactose into the glycolysis pathway. Copyright 2016 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it.
eBook - ePub- Sheldon Reiser(Author)
- 2018(Publication Date)
- CRC Press(Publisher)
Table 1 ). When rats were fed 65% glucose, glucose uptake of the jejunum was significantly greater than when rats consumed a diet containing 30% glucose. Consuming a diet of 65% fructose stimulated fructose uptake in both the jejunum and the ileum. In the rat intestine, since there is no glucose-6-phosphatase, there is little conversion of fructose to glucose.II. Initial Steps of Fructose Metabolism
The initial step in the metabolism of fructose is shown in Figure 1 . Fructose is phosphorylated by fructokinase16 - 19 to fructose-1-phosphate. This reaction requires Mg+ + , ATP, and K+ .20 , 21 Fructokinase can also catalyze the phosphorylation of some other ketoses, including galactoheptulose, sorbose, tagatose, and xylulose. Affinity is dependent on the amount of potassium.19 , 20 Fructose-1-phosphate accumulates rapidly in the liver as a result of the phosphorylation of fructose by fructokinase.21The second reaction in the metabolism of fructose is the splitting of fructose-1-phosphate by fructose-1-phosphate aldolase to dihydroxyacetone phosphate and glyceraldehyde (Figure 2 ).22 , 23 This enzyme can also cleave fructose-1,6-diphosphate and work in the opposite direction to condense the two triose phosphates, dihydroxyacetone phosphate and glyceraldehyde-3-phosphate, into fructose-1,6-diphosphate.24 Aldolases occurring in brain and muscle have a much lower affinity for fructose-1-phosphate than does liver aldolase,25 in which the affinity of the enzyme for fructose-1-phosphate is not different from its affinity for fructose-1,6-diphosphate.26 Formation of dihydroxyacetone phosphate and glyceraldehyde from fructose-1-phosphate was confirmed by labeling fructose with 14 C in both the 1-C and 6-C positions.27Figure 3 depicts the diverse fates of dihydroxyacetone phosphate. It can be isomerized to glyceraldehyde phosphate and continue through the glycolytic pathway28 , 29 to yield ultimately either lactic acid (anaerobic conditions) or acetyl CoA (aerobic conditions) from pyruvate. The acetyl CoA could then enter the TCA cycle or be used for fatty acid synthesis. Dihydroxyacetone phosphate can also be reduced to glycerol-3-phosphate which can provide the glycerol moiety of triglycerides. Alternatively, dihydroxyacetone phosphate can be condensed with glyceraldehyde-3-phosphate by fructose-1,6-diphosphate aldolase to form fructose-1,6-diphosphate and ultimately glucose or glycogen. Förster30
eBook - PDF- Dmitry Murzin, Olga Simakova(Authors)
- 2015(Publication Date)
- Royal Society of Chemistry(Publisher)
On the contrary, under thermo-chemical conditions at lower temperatures ( o 250 1 C), catalysts are used to obtain sugars in higher quantities by subjecting substrates to hydrolysis. Considering this, in this chapter, discussions are focused on the conversion of di/ polysaccharides into sugars by hydrolysis reactions. In the conversion of lignocelluloses to chemicals, multiple steps are involved and these are de-picted in Figure 1.1. Conversion of Biomass into Sugars 3 1.1.1 Potential Source of Sugars Monosaccharides, or else we call them sugars, are named in two ways: (1) a monosaccharide containing an aldehyde group is called aldose and (2) a monosaccharide containing a ketone group is called ketose. In total, eight C 6 aldo-sugars (glucose, mannose, galactose, allose, altrose, gulose, idose and talose) and four C 5 aldo-sugars (xylose, arabinose, ribose and lyxose) are structurally possible. Besides these aldo-sugars, two more keto-sugars viz. fructose and xylulose are also well-known in nature. But, among them, idose and talose are not found in nature. Moreover, the presence of allose, altrose, gulose, ribose and lyxose is very rare in nature and hence discussions on those are not made here. The rest of the sugars are generally present in fruits, edible plants, living bodies, bacteria, proteins etc . In Figure 1.2, likely sources of main C 6 sugars (glucose, fructose, man-nose, galactose) and C 5 sugars (xylose, arabinose, xylulose) are illustrated. In general, these monosaccharides (sugars) can be obtained by the hydrolysis (addition of one mole of water per 2 moles of sugars) of their respective disaccharides [maltose: a -1,4-D -glucose disaccharide (found in potatoes, cereal, beverages etc. ), cellobiose: b -1,4-D -glucose disaccharide, sucrose: di-saccharide of a -D -glucose and b -D -fructose linked via a 1,2 glycoside bond (found in sugarcane, beet, grains etc. ), xylobiose: b -1,4-D -xylose disaccharide etc. ].
eBook - ePub- P. M. Dey, J. B. Harborne(Authors)
- 1997(Publication Date)
- Academic Press(Publisher)
−1 .Glucose-6-phosphate is also available to the plant from the isomeric glucose-1-phosphate, which is produced either by the hydrolysis of sucrose (Chapter 4 ) or as one of the products of starch breakdown. The interconversion of glucose-1-phosphate to the 6-phosphate is catalyzed by phosphoglucomutase (or glucose phosphate mutase) in a reversible reaction which shows only a small change in standard free energy (–7.0 kJ mol−1 ). The optimum pH is 7.5 for this reaction, during which a phosphate ion is transiently attached to a serine side chain of the enzyme.The first committed step of glycolysis is the conversion of glucose-6-phosphate into fructose-6-phosphate in a reversible reaction catalyzed by hexose phosphate isomerase:Scheme 1This is an interesting interconversion by which a hexose, glucose, which takes up the pyranose configuration, is changed to a keto sugar, fructose, which has a furanose configuration.The second step in glycolysis is the phosphorylation with organic phosphate, of fructose-6 phosphate to produce fructose 1,6-bisphosphate. This is catalyzed by phosphofructokinase in the presence of ATP in an irreversible reaction (Scheme 2 ).Scheme 2There is a second enzyme, fructose-6-phosphate: pyrophosphate phosphotransferase, present in the cytosol which is capable of carrying out the same reaction, with pyrophosphate instead of ATP as the other substrate. It operates with only a small change in standard free energy (ΔG°′ – 2.9 kJ mol−1 ) and hence is readily reversible. Whether it has a role in glycolysis is still debatable. Its importance to carbohydrate metabolism appears to lie more in the reverse reaction, by which fructose-1,6-bisphosphate is hydrolyzed to supply pyrophosphate for sucrose breakdown via UDP-glucose pyrophosphorylase (see Chapter 4
- B C Currell, R C E Dam-Mieras(Authors)
- 2017(Publication Date)
- Butterworth-Heinemann(Publisher)
The biosynthesis of carbohydrates 157 6.3 The biosynthesis of hexoses, pentoses and tetroses sugar inter-conversions The most important hexose sugar is glucose though several others, notably fructose, galactose and mannose are very widespread. In addition other sugars, for example rhamnose, have a more restricted distribution and others are possibly unique to a given species of bacterium. Sometimes sugars require attachment to a carrier molecule before interconversion can occur, the usual carrier being uridine diphosphate (UDP) or occasionally thymidine diphosphate (TDP). Figure 6.5 shows a simplified diagram detailing the production of hexoses from gluconeogenic intermediates. Many more intermediates are found in living systems particularly as the diagram includes examples of oxidised sugars (glucuronic acid) and substituted sugars (glucosamine). The purpose of the diagram is to indicate that living systems generally can produce hexose derivatives with relative ease from the central glucose and fructose precursors. Note the key ('Central') position of fructose-6-phosphate. N-acetyl glucosamine-1-phosphate t N-acetyl glucosamine-6-phosphate . t . glucosamine-6-phosphate mannose-6-phosphate« mannose pyruvate gluconeogenesis 1 fructose-6-phosphate glucose-6-phosphate -glucose-1-phosphate UDP-glucos e Ψ UDP-galactose Ψ galactose-1-phosphate galactose allose t allose-6-phosphate allulose-6-phosphate * mannitol glucose UDP-glucuronate Figure 6.5 The biosynthesis of hexoses, hexitols and other carbohydrate derivatives from gluconeogenic precursors. 158 Chapter 6 Pentose sugars are produced generally by the pentose phosphate pathway (as are tetroses) which yields ribose-5-pkosphate, ribulose-5-phosphate and xylulose-5-phosphate following oxidative decarboxylation of glucose. As with hexoses, interconversion of pentoses is readily achieved with the central intermediate appearing to be xylulose-5-phosphate.
eBook - ePubBiomass, Biofuels, Biochemicals
Recent Advances in Development of Platform Chemicals
- S. Saravanamurugan, Hu Li, Anders Riisager, Ashok Pandey(Authors)
- 2019(Publication Date)
- Elsevier(Publisher)
Chapter 2Glucose oxidation to carboxylic products with chemocatalysts
Nidhi Aggarwal, Muhamad Aadil Yatoo, and Shunmugavel Saravanamurugan Laboratory of Bioproduct Chemistry, Center of Innovative and Applied Bioprocessing, Sector-81 (Knowledge City), Mohali, Punjab, IndiaAbstract
This chapter presents recent developments on the conversion of a biomass-derived monosaccharide, that is, glucose, to selective oxidation products, such as gluconic acid, glucaric acid, and formic acid. These oxidation products are deemed to be potential platform chemicals because they have a wide range of applications in the food, pharmaceutical, and textile industries. This chapter especially covers recent research publications for the production of those oxidation products from glucose with metal-containing chemocatalysts, including nonprecious metals, and their applications. The chapter describes further how the reaction parameters, such as oxidants (O2 , air, and peroxides), temperature, and time, influence the yield of target products under aqueous conditions. It also briefly includes the use of homogeneous catalysts for the transformation glucose to its oxidation products.Keywords
Chemocatalysts; Formic acid; Glucaric acid; Gluconic acid; Glucose; Oxidation1. Introduction
A great deal of attention has been paid to valorizing terrestrial biomass as renewable and inexpensive feedstock for producing chemicals and fuels for replacing fossil-based ones [1] . In this regard, efficient conversion of the cellulosic part of biomass to glucose and then to various value-added products thus becomes more attractive. However, selective production of glucose from cellulose is highly challenging due to its minimal solubility in water and/or organic solvents. On the other hand, the valorization of glucose to its oxidation products, such as gluconic acid, glucaric acid, and formic acid, is quite interesting and promising [2 –4 ]. Over the past decade, the development of an efficient catalytic system for glucose oxidation reactions has been the subject of great interest in terms of improving the activity, selectivity, yield, and stability of metal catalysts [5 –7
Index pages curate the most relevant extracts from our library of academic textbooks. They’ve been created using an in-house natural language model (NLM), each adding context and meaning to key research topics.
